(a) But-3-en-2-ol The following questions are multiple choice questions. Choose the most appropriate (b) But-2-en-2-ol answer: (c) Prop-2-enol (i) Which of the following is the product of reactions? (d) Butan-2-ol OH ? (iii) Benzyl alcohol on treatment with this copper- based catalyst gives a compound ‘A’ which on NiO2 / CH3COOH reaction with KOH gives compounds ‘B’ and n-hexane ‘C’. Compound ‘B’ on oxidation with KMnO4– KOH gives compound ‘C’. Compounds ‘A’, ‘B’ OH O and ‘C’ respectively are: (a) H (b) H (a) Benzaldehyde, Benzyl alcohol, potassium salt of Benzoic acid H COOH (b) Benzaldehyde, potassium salt of Benzoic (c) (d) acid, Benzyl alcohol O (c) Benzaldehyde, Benzoic acid, Benzyl (ii) The product of reaction when aniline is alcohol subjected to nickel based catalyst: (d) Benzoic acid, Benzyl alcohol, CN NH Benzaldehyde (a) (b) 2 (iv) An organic compound ‘X’ with molecular (c) (d) N N formula C3H8O on reaction with this copper based catalyst gives compound OR ‘Y’ which reduces Tollen’s reagent. ‘X’ on Monochlorination of toluene in sunlight reaction with sodium metal gives ‘Z’ . What followed by hydrolysis with aq. NaOH yields. is the product of reaction of ‘Z’ with 2-chloro- 2-methylpropane? (a) o-Cresol (b) m-Cresol (c) 2, 4-Dihydroxytoluene (a) CH3CH2CH2OC(CH3)3 (d) Benzyl alcohol (b) CH3CH2OC(CH3)3 (iii) Benzyl chloride on hydrolysis with NaOH (c) CH2=C(CH3)2 (aq.) gives product ‘X’ which on reaction with (d) CH3CH2CH=C(CH3)2 NiO2 in presence of CH3COOH in n-hexane, 2. Case Study gives compound ‘Y’. Compound Y is A variety of aromatic alcohols were efficiently oxidized to their corresponding aldehydes and O ketones in good to excellent yields using nickel OH peroxide activated by acetic acid. Some thiols and amines were also readily oxidized by this oxidant (a) (b) under mild conditions. The oxides and oxyanions O of vanadium, chromium, manganese and even iron have proven to be useful oxidants. We have H (d) CH3 observed that the oxidation of a series of alcohols to aldehydes and ketones, oxidative coupling of (c) thiols to disulfides and oxidation of some amines proceed rapidly and efficiently by nickel peroxide (iv) What would be ‘B’? in the presence of acetic acid. Treating of n-hexane solution of aniline with nickel peroxide in the NH2 O presence of acetic acid afforded the corresponding (a) (b) diazo compound. O OH O (c) (d) 3. Case Study NiO / CH COOH + NiO + H2O Higher alcohols are important compounds 23 with widespread applications in the chemical, n-hexane (Source: Mohammad Kooti and Mehdi Jorfi, 2008, Mild and Efficient Oxidation of Aromatic Alcohols and Other Substrates Using NiO2/CH3COOH System, E-Journal of Chemistry, 5(2), 365-369) 250 Chemistry-12
pharmaceutical and energy sectors. Currently, (d) Assertion is wrong statement but reason is they are mainly produced by sugar fermentation correct statement. (ethanol and isobutanol) or hydration of petroleum- derived alkenes (heavier alcohols), but their direct (i) Assertion: Higher alcohols are produced asymntohreesiesnfvriormonsmynegnatasl(lCy-Ofr+ienHd2)lyw, ovuelrdsacotimleparinsde in industries by sugar fermentation. economical alternative. Research efforts in this reaction, initiated in the 1930s, but no catalytic Reason: Higher alcohols are produced system reported to date has performed sufficiently in industries by hydration of petroleum- well to justify an industrial implementation. derived alkenes. Rh-based, Mo-based, modified Fischer–Tropsch and modified methanol synthesis catalysts are (ii) Assertion: Direct synthesis of higher the recent advances in the catalytic systems to alcohols from syngas have some prepare higher alcohols from syngas. But there advantages as compared to conventional is scope to improve the efficiency of reactors and methods used in industries. separation units as well as to utilise CO2 and recycle side-products in the process to perform Reason: Synthesis from syngas is them up to the mark for industrial use. more environment friendly, versatile (Reference: Ho Ting Luk, Cecilia Mondelli, Daniel and economical. Curulla Ferre, Joseph A.Stewart and Javier Perez- Ramirez, 2017, Status and prospects in higher (iii) Assertion: Rh-based catalyst do alcohols synthesis from syngas, Chemical Society sufficiently well in direct synthesis Reviews, 46(5), 1358-1426) of higher alcohols from syngas to use In these questions, a statement of assertion industrially. followed by a statement of reason is given. Choose the correct answer out of the Reason: Rh (rhodium) a transition following choices. elements acts as catalyst due to variable (a) Assertion and reason both are correct oxidation states. (iv) Assertion: Modified Fischer–Tropsch statements and reason is correct explanation and modified methanol synthesis do not for assertion. justify an industrial implementation for (b) Assertion and reason both are correct higher alcohol production. statements but reason is not correct Reason: These processes need to improve explanation for assertion. the efficiency of reactors and separation (c) Assertion is correct statement but reason is units, also needs to utilise CO2 evolved wrong statement. and recycle by-products. OR Assertion: Syngas is the mixture of carbon monoxide and hydrogen gas. Reason: Water gas is the mixture of carbon monoxide and hydrogen gas. 1. (i) (d) (ii) (b) OR (a) (iii) (b) (iv) (c) Answers (ii) (a) (iii) (d) (iv) (a) OR (b) 2. (i) (c) (ii) (d) OR (d) (iii) (c) (iv) (b) 3. (i) (b) Analogy based questions 2. Complete the following analogy: 1. Which of the following analogies is correct? Alcohols : A : : Ethers : B (i) 1° alcohol with Lucas reagent : Turbidity (i) A : Hydrogen bonding with water, B : No appears immediately : : 2° alcohol with hydrogen bonding with water Lucas reagent : Turbidity appears after 5 (ii) A : Hydrogen bonding among their minutes molecules, B : No hydrogen bonding among (ii) Catechol : It has two —OH group : : Cresol : their molecules It has one —OH group (iii) A : C—O—H bond angle is greater than (iii) o-Nitrophenol : More soluble in water : : tetrahedral angle, p-Nitrophenol : Less soluble in water B : C—O—H bond angle is less than (iv) Phenetole : Methoxybenzene : : Anisole : tetrahedral angle, Ethoxy benzene (iv) A : Higher pKa value, B : Lower pKa value Answers 1. (ii) 2. (ii) alCohols, phenols and ethers 251
Matching type questions 1. Match the starting materials given in Column I with the products formed by these (Column II) in the reaction with HI. Column I Column II A. CH3 O CH3 (1) OH + CH3I B. CH3 CH O CH3 (2) CH3 C I + CH3OH CH3 CH3 C. H3C CH3 CH3 CH3 CO (3) I + CH3OH CH3 OCH3 (4) CH3 OH + CH3 I D. (5) CH3 CH CH3 OH + CH3I CH3 CH I + CH3OH CH3 (6) CH3 (7) CH3 C OH + CH3I CH3 (i) A (4) B (5) C (1) D (2) (ii) A (6) B (5) C (7) D (3) (iii) A (4) B (5) C (2) D (1) (iv) A (6) B (5) C (7) D (1) 2. Match the items of column I with items of column II. Column I Column II A. Antifreeze used in car engine (1) Neutral ferric chloride B. Solvent used in perfumes (2) Glycerol C. Starting material for picric acid (3) Methanol D. Wood spirit (4) Phenol E. Reagent used for detection of phenolic group (5) Ethlene glycol F. By product of soap industry used in cosmetics (6) Ethanol (i) A (2) B (6) C (5) D (3) E (1) F (4) (ii) A (5) B (6) C (4) D (3) E (1) F (2) (iii) A (6) B (4) C (5) D (3) E (2) F (1) (iv) A (2) B (5) C (6) D (4) E (1) F (3) 252 Chemistry-12
3. Match the items of column I with items of column II. Column I Column II A. Methanol (1) Conversion of phenol to o-hydroxysalicylic acid B. Kolbe’s reaction (2) Ethyl alcohol C. Williamson’s synthesis (3) Conversion of phenol to salicylaldehyde D. Conversion of 2° alcohol to ketone (4) Wood spirit E. Reimer-Tiemann reaction (5) Heated copper at 573K F. Fermentation (6) Reaction of alkyl halide with sodium alkoxide (i) A (4) B (1) C (6) D (5) E (3) F (2) (ii) A (4) B (6) C (5) D (1) E (2) F (3) (iii) A (2) B (6) C (1) D (5) E (4) F (3) (iv) A (2) B (6) C (4) D (5) E (1) F (3) 1. (iii) 2. (ii) Answers 3. (i) Quick revision notes • In allylic alcohols, the —OH group is attached to • Alcohols and phenols are formed when a hydrogen atom in hydrocarbon, aliphatic and aromatic the sp3 hybridised carbon, but it is next to C==C respectively, is replaced by hydroxyl group (–OH, double bond, e.g. CH2=CH–CH2OH is allyl alcohol. e.g. CH3OH, C6H5OH group). • In vinylic alcohol, —OH group is bonded to sp2 hybridised carbon, e.g., CH2 = CH—OH. • Alcohols are usually classified as primary (1°), • In benzylic alcohol, —OH group is bonded to sp3 secondary (2°) or tertiary (3°) alcohols. hybridised carbon but next to an aromatic ring • In primary alcohols, –OH group is attached CH2OH . to 1° carbon, e.g. CH3CH2OH whereas in e.g., secondary alcohol –OH is attached to 2° CH3 carbon, e.g. CH3 CH–OH whereas in 3° alcohol • Alcohols are prepared by acid catalysed hydration of alkenes (following Markonikov addition), by –OH group is attached to 3° carbon, e.g. hydroboration oxidation reaction (following anti- Markovnikov’s addition), by reduction of carbonyl (CH3)3COH. compounds and from carboxylic acids and esters, • Phenols could have mono, di or trihydroxy by hydrolysing alkyl halides using a mild base Gorribgynahrdydrreoalgyesnint agnedtbhyertrsea(utisninggprHim2SaOry4)a,mfrinoems derivatives depending on whether there are one, with nitrous acid. two, three or more —OH groups attached to the • Phenols can be prepared by substitution of OH OH halogen atom in haloarenes, sulphonic acid OH . group in aryl sulphonic acids with –OH group. phenyl ring structure, e.g. , OH It can also be prepared by hydrolysing benzene diazonium salts and industrially from cumene. • Analogous to alcohols and phenols, ethers are • Alcohols with low molecular mass are colourless classified on the basis of number of groups lliiqquuiiddss,amnoddheirgahteermmasesm(bi.eer.sCa5-rCe1w1 garxoyupso)laidres.oily attached to the –O at om, e. g. CH3OCH3 is • Alcohols and phenols generally have higher boiling OCH3 is 1,1-dimethoxy points than the corresponding hydrocarbons, dimethyl ether, CH3–CH OCH3 ethers, haloalkanes/ arenes due to their ability ethane. to form intermolecular hydrogen bonds. • Alcohols are named according to the IUPAC • The ability of alcohols and phenols to make system by replacing ‘e’ of the parent hydrocarbon intermolecular hydrogen bonds makes them chain with ‘ol’, e.g. CH3CH2CH2OH is 1-propanol. soluble in water; however members with high • Alcohols too like phenols may have more than alCohols, phenols and ethers 253 –OH group. Such compounds are referred as dihydric, trihydric or polyhydric alcohols, e.g. OH HOCH2–CH2OH, HOCH2–CH–CH2OH.
molar masses are less soluble/ insoluble due to • Methanol is mainly used for preparing formaldehyde which is of great industrial large hydrocarbon-solvent repelling group. importance. It is also used for preserving biological specimens in biological labs and • Phenol is also called carbolic acid. It should not for making bakelite, urea formaldehyde and melamine formaldehyde resin. be touched. • Ethanol is commercially prepared by fermentation • Alcohols and phenols are acidic in nature but of glucose and fructose and is of great industrial and commercial use. It is used in cough syrups phenols are more acidic than alcohols due to and tonics. stable phenoxide ion. • Ethers are the organic compounds in which two alkyl or aryl groups are attached to a divalent • If an electron withdrawing group is attached to oxygen known as ethereal oxygen, e.g. C2H5OC2H5 (Diethyl ether) the benzene ring in phenol, then it increases its • In the IUPAC system, ethers are regarded as acidic strength (e.g. –NO2, –Cl, –Br, –I) ‘alkoxyalkanes’ in which the ethereal oxygen is • On the contrary, electron donating group taken along with smaller alkyl group while the bigger group is considered as a part of alkane, e.g. decreases the acidity of phenol and its derivatives CH3OCH2CH3 is methoxyethane. (–CH3, –OCH3) • Ethers are either prepared by dehydration of • Alcohols can undergo nucleophilic substitution alcohols at 413 K or by Williamson’s synthesis, in which only primary alcohol can form ether, via reactions with halogen acids or hydrogen halides SN2 mechanism. to yield alkyl halides by iSnN32° mechanism in 1° • Ethers are polar but insoluble in water with alcohols, SN1 mechanism alcohols. boiling points comparable to that of corresponding alkanes, but less than the corresponding alcohols • The primary, secondary and tertiary alcohols can due to their inability fo form H-bonds be distinguished by treating them with Lucas • In ethers, the C-O bond can be cleaved using hydrogen halides by electrophilic substitution reagent (conc. HCl and ZnCl2) in the Lucas test. reactions. • Alcohols can also undergo dehydration reaction • Ethers with two different alkyl groups are also twoitfhorcmonacl.kHen2SeOs.4 EorthHa3nPoOl 4g,iovresbydiuestihnygl alumina cleaved in the same manner and this results in the ether on formation of primary halide by SN2 mechanism. heating at 413 K with conc. H2SO4. • In case of tertiary alkyl group, SN1 mechanism • With mild oxidising agents, alcohols are oxidised is followed for alkyl halide formation. to form aldehyde and with strong oxidising • In aromatic ethers, the C-O bond activates the aromatic ring towards electrophilic substitution agents, they form carboxylic acids. at o, p-positions, e.g. Anisole gives o and p-isomers on electrophilic substitution. • In phenols the –OH group activates the aromatic ring to undergo electrophilic substitution reactions at o, p-positions with respect to the –OH group, due to resonance effect. • Salicaldehyde (2-hydroxybenzaldehyde) is formed by Reimer –Tiemann reaction of phenols. • On treating with chloroform in the presence of an alkali like NaOH, phenol undergoes Kolbe’s reaction to form salicylic acid (2-hydroxybenzoic acid). • Methanol and ethanol are the commercially important alcohols. ImPortAnt rEActIons 1. CH3Cl + KOH(aq) CH3 OH + KCl 2. CO + 2H2 ZnO - Cr2 O3 CH3OH Methanol 200 - 300 atm 573 - 673 K 3. Hydroboration oxidation: 6CH3—CH=CH2 + B2H6 2(CH3CH2CH2)3B H2 O2 6CH3CH2CH2OH + H3BO3 OH– O 4. CH3—CH=CH2 + H2O H2 SO4 CH3—CH—CH3 5. CH3—C—Hr LiAlH4 CH3 CH2 OH OH o H2 /Pd Ethanol Ethanal 2-propanol O LiAlH4 OH 6. CH3—C—CH2—CH3 or NaBH4 CH3—CH—CH2—CH3 Butan-2-one Butan-2-ol 254 Chemistry-12
O O OH CH CH2OH C CH3 CH CH3 7. LiAlH4 8. LiAlH4 r o H2 /Pd or NaBH4 Benzaldehyde Benzyl alcohol Acetophenone 1-phenylethanol (Phenyl methanol) O OMgBr H2 O/H+ CH3 CH2 OH + Mg Br 9. H—C—H + CH3MgBr H—C—H Ethanol OH Methanal CH3 O OMgBr H2 O/H+ OH Br 10. CH3—C—H + CH3MgBr CH3—CH—CH3 CH3—CH—CH3 + Mg OH Propan-2-ol Ethanal O OMgBr H2 O/H+ OH Br 11. CH3—AcCet—onCe H3 + CH3MgBr CH3—C—CH3 + Mg OH CH3—C—CH3 CH3 CH3 12. Oxoprocess: CH2 = CH2 + CO + H2 [Co (CO) 4] 2 CH3 CH2 CHO + H2 Ni CH3 CH2 CH2 OH Ethene Propanal 1 - Propanol O 13. CH3—C—OH LiAlH4 CH3CH2OH COOH CH2OH 14. LiAlH4 + H2O 15. CH3COOC2H5 + H2O H+ CH3COOH + C2H5OH Cl OH 16. CH3CH2NH2 + HNO2 CH3CH2OH + N2 + H2O 17. + NaOH 623 K, 300 atm + NaCl OH H+ OH NH2 N+2Cl– SO3H 18. NaNO2 H2 O + N2 + HCl 19. Oleum (i) NaOH +HCl Warm (ii) H+ H2 O/H+ CH3—CH—CH3 CH3 OH O CH3—C—O—O—H 20. + O2 Heat + CH3—C—CH3 Air Cumene Cumene hydroperoxide Phenol Acetone 21. CH3 CH2 OH conc H2 SO4 CH2 = CH2 + H2 O 22. 2CH3CH2OH conc H2 SO4 CH3 CH2 OCH2 CH3 + H2 O Ethanol 443 K Ethene 413 K Diethyl ether 23. CH3—CH—CH3 80% H3 PO4 CH3 —CH = CH2 + H2 O 440 K OH CH3 20% H3 PO4, 358 K CH3 24. CH3—C—CH3 or Cu, 573 K CH3—C = CH2 + H2O OH O OH O CH3—C—CH3 + H2 25. CH3CH2OH Cu CH3—C—CH3 + H2 26. CH3—CH—CH3 Cu 573 K 573 K CH2OH COOH 27. CH3CH2OH KMnO4/dil H2SO4 CH3COOH 28. KMnO4/dil H2SO4 alCohols, phenols and ethers 255
29. CH3CH2OH CrO3 CH3CHO 30. CH3—CH = CH—CH2OH PCC CH3—CH = CH—CHO 32. C2H5OH PCl5 C2H5Cl + POCl3 + HCl 31. CH3—CH—CH3 CrO3 CH3—C—CH3 OH CH2Cl O CH2OH 33. SOCl2 + SO2 + HCl 34. CH3COOH + C2H5OH H+ CH3COOC2H5 + H2O COOH COOCH3 35. + CH3OH H+ + H2O 36. C2H5—OH + NH3 Al2 O3 C2H5NH2 + H2O ' Benzoic acid Methyl benzoate OH 37. + Zn (dust) + ZnO 38. 2C2H5OH + 2Na 2C2H5ONa + H2 OH ONa OH ONa 39. 2 + 2Na 2 + H2 40. + NaOH + H2O 41. Kolbe’s Reaction: CO2 OH O H+ OH OH ONa heat, 3 - 7 atm C—ONa COOH NaOH 42. ReOiHmer Tiemann Reaction: OH Salicylic acid + CHCl3 + 3KOH 340 K CHO + 3KCl + 2H2O OH O OCOCH3 43. + CH3—C—Cl NaOH + HCl Phenyl ethanoate OH OCOCH3 COOH 44. COOH NaOH + CH3COOH + (CH3CO)2O Aspirin OH OH COOCH3 + H2O COOH conc. H2 SO4 ' 45. + CH3OH Methyl salicylate (Iodex) 46. C12H22O11 +H2O Invertase→ C6H12O6 + C6H12O6 Glucose Fructose C6H12O6 Zymase → 2C2H5OH + 2CO2 OH O 47. Na2 Cr2 O7 conc. H2 SO4 256 O p-benzoquinone Chemistry-12
48. Electrophilic substitution reactions: OH OH OH + Br2 CS2 Br 273 K + 2-bromophenol Br (Minor) 4-bromophenol (Major) OH OH OH OH OH 49. + dil. HNO3 NO2 50. + 3Br2(aq) Br Br + + 3HBr o-nitrophenol NO2 Br (Minor) p-nitrophenol 2,4,6-Tribromophenol (Major) OH O2N OH NO2 51. + conc. 3HNO3 NO2 (Picric acid) 2,4,6-Trinitrophenol OH OH OH 52. + conc. H2SO4 heat SO3H + 2-hydroxy SO3H benzeneacsiudlphonic 4-hydroxy benzeneacsiudlphonic 53. Friedel Crafts Alkylation: CH3 + OH OH OH + HCl + CH3Cl AlCl3 (o-cresol) CH3 (p-cresol) 2-methylphenol 4-methylphenol 54. Friedel Crafts Acylation reaction: OH OH OH O + CH3—C—Cl AlCl3 COCH3 + 2-hydroxy COCH3 acetophenone 4-hydroxy acetophenone 55. Williamson Synthesis: OCH3 ONa + CH3I + NaI Methoxy benzene (Anisole) CH3 CH3 + NaI 56. CH3—C—ONa + CH3I CH3—C—OCH3 CH3 CH3 2-methoxy-2-methyl propane alCohols, phenols and ethers 257
57. CH3OC2H5 + HI C2H5OH + CH3I 58. CH2OCH3 + HI CH2I + CH3OH CH3 CH3 60. OCH3 OH 59. CH3—C—OCH3 + HI CH3—C—I + CH3OH + HI + CH3I CH3 CH3 OCH3 OCH3 OCH3 OCH3 61. + Br2 CH3COOH Br + (Minor) Br (Major) OCH3 OCH3 OCH3 62. + conc. HNO3 conc. H2SO4 NO2 + (Minor) NO2 (Major) OCH3 OCH3 OCH3 63. + CH3Cl AlCl3 CH3 + (Minor) CH3 (Major) OCH3 O OCH3 COCH3 64. + CH3—C—Cl AlCl3 + 2-methoxy acetophenone COCH3 (Minor) 4-methoxy acetophenone (Major) common Errors Errors corrEctIons (i) Students are not able to identify the primary, secondary Primary: R—CH2—OH R—CH—OH and tertiary alcohols correctly. Secondary: | Tertiary: R R | R—C—OH | R (ii) Normally students write wrong resonating structures. Movement of electrons in the benzene ring can be practiced. (iii) Students are not clear about the suitable conditions The mechanism of reaction must be known required for the Williamson reaction (alkyl halide must be to the students to decide the conditions. primary one and the sodium salt of tertiary alcohols should be taken. 258 Chemistry-12
rEvIsIon chArt Classification Alcohols • Alcohols are classified as primary (1º), These are the organic compounds formed by the replacement of H-atom of hydrocarbon chain with secondary (2º) and tertiary (3º) alcohols, –OH group. depending upon the type of C-atom to which –OH group is attached. • Alcohols are also classified as mono, di or polyhydric alcohols, depending upon the no. of –OH groups present. Chemical Properties • Alcohols due to polar O–H group are acidic in nature. Nomenclature • Alcohols can easily undergo nucleophilic substitution In the IUPAC system, alcohols are named reaction with hydrogen halides to form haloalkanes. by replacing‘e’of the parent hydrocarbon chain with ‘–ol’. • Dehydration of alcohols can give alkenes. Preparation • In the presence of mild oxidising agents like PCC, • By hydration of alkenes in the presence Cu at 573 K, 1° and 2° alcohols give aldehydes and ketones respectively. of an acid or by hydroboration oxidation reaction; • On strong oxidation, alcohols form carboxylic acids. • By reduction of carbonyl compounds or by action of Grignard reagent on it. • Tertiary alcohols are generally resistant to oxidation and form alkene. Physical Properties • Alcohols are higher boiling liquids than other • Methanol and Ethanol are two commercially important alcohols of great use in industries. classes of organic compounds of comparable molecular masses; namely ethers, haloalkanes, or • We can easily distinguish between primary, hydrocarbons. secondary and tertiary alcohols using Lucas test as: • This is due to extensive intermolecular H-bonding among the alcohol molecules. It also make them R–OH (1°) No turbidity at water soluble. room temperature R–OH + HCl conc. HCl+ ZnCl2 R–OH (2°) Turbidity appears after 5 minutes Turbidity appears R–OH (3°) immediately alCohols, phenols and ethers 259
rEvIsIon chArt Nomenclature Phenols Preparation In the IUPAC system, simplest It is an aromatic Phenols can be prepared (i) hydroxy derivative of benzene compound formed by Industrially from cumene, (ii) by is named phenol. Derivatives replacement H-atom substitution of X-atom in haloarenes of phenols are referred to the of a benzene ring. oarcidSsO. 3H group in arenesulphonic compounds having substitution at –o and –p positions wrt the penolic Chemical Properties ring. • Phenol is more acidic than alcohols. Electron Physical Properties donating groups increases while electron • Phenol and its derivatives are withdrawing groups decreases the acidic strength of phenols. colourless crystalline solids or liquids and they are water soluble • The presence of O–H group in phenols activates due to the ability to form extensive the benzene ring towards electrophilic intermolecular and intramolecular substitution reactions, preferably at o- and H-bonds. p-positions, due to resonance effect. • They have comparatively higher melting and boiling points • Reimer-Tiemann reaction of phenol yields than other classes of organic salicylaldehyde. compounds with comparable molecular masses. • On reaction with Na metal, phenol forms phenoxide ion, which is more reactive than phenol and in alkaline medium it can undergo Kolbe’s reaction. • Phenol can be distinguished from alcohols by using naelcuothraollsFedCol3n sootl.ution. It gives violet colour while Nomenclature Ethers Preparation Ethers are named as alkoxyalkanes They are prepared by dehydration of as per IUPAC nomenclature. The These are the organic alcohols or by Williamson’s synthesis. bigger hydrocarbon chain forms the compounds with parent chain and smaller alkyl group formula R–O–R’. Chemical Properties constitutes, the alkoxy group. If R = R’ then it is The C–O–bond can either symmetrical ether and undergo cleavage or electrophilic Physical Properties if these alkyl groups substitution reaction which occur at Boiling point of ethers in are different then it is o and p- positions in aromatic ethers. comparatively low as compared to unsymmetrical ether. the compound with comparable molecular mass i.e. alcohols, due to absence of intermolecular H-bonding. 260 Chemistry-12
chAPtEr trEnd—Based on Past Years’ cBsE Exams ➣ It has been observed from this chapter that the weightage of topics ‘Alcohols’ and ‘Phenols’ (especially, their chemical properties) are maximum. Hence, these are most important topics. ➣ From this chapter , generally 1 mark questions were asked from the topic ‘Phenols’. ➣ Most of the 2 and 3 marks questions from this chapter belong to the topic ‘Alcohols’. Questions For Practice (1 Mark) [AI 2017] Very Short Answer Type Questions 1. Write IUPAC name of the following compounds OH NO2 NO2 [Delhi 2017(C)] 2. What happens when phenol is oxidised by Na2Cr2O7/ H2SO4? [AI 2017] 3. What happens when Phenol is treated with Zn dust? (2 Marks) Write chemical equations in support of your answer. [AI 2017] 4. Write the product in the following reaction: [Delhi 2017] OH [Delhi 2015] COOH (CH3 CO)2 O (3 Marks) H+ ? [Delhi 2017(C)] 5. Arrange the following compounds in increasing order of the property indicated. (i) p-nitrophenol (ii) ethanol (iii) phenol (acidic character) 6. Name the reagents used in the following reaction: Nitration of phenol to 2,4,6-trinitrophenol Short Answer Type Questions-I 7. (i) Write IUPAC name of the following compound C6H5—CH2—CH2—OH (ii) What happens when (CH3)3C—OH is treated with Cu at 573 K. 8. Give simple chemical tests to distinguish between the following pair of compounds. (i) Ethanol and phenol (ii) Propanol and 2-methylpropan-2-ol 9. Write the formula of the reagents used in the following reactions: (i) Butanal to butanol (ii) Hydroboration of propene and then oxidation to propanol. 10. How will you convert the following: (i) Propan-2-ol to 2-methyl propan-2-ol (ii) Formaldehyde to propanol Short Answer Type Questions-II 11. Explain the mechanism for hydration of acid catalysed ethene: CH2=CH2 + H2O H+ CH3—CH2OH 12. Write the main product(s) in each of the following reactions: (i) B2 H6 (i) CH3—CH=CH—CH2—OH PCC ? (ii) CH3—CH=CH2 (ii) 3H2 O2 /OH– (iii) CH3CH2CH2—CHO + H2 Pd ? alCohols, phenols and ethers 261
AssIgnmEnt Time: 45 Minutes M.M.: 25 Multiple Choice Questions (MCQs) (1 Mark) 1. Monochlorination of toluene in sunlight followed by hydrolysis with aq. NaOH yields (i) o-Cresol (ii) m-Cresol (iii) 2, 4-Dihydroxytoluene (iv) Benzyl alcohol 2. Which of the following species can act as the strongest base? (i) OH (ii) OR (iii) O–C6H5 (iv) m- O–C6H4 (NO2) 3. The correct order of decreasing acid strength of the following compounds is (i) (E) > (D) > (B) > (A) > (C) (ii) (B) > (D) > (A) > (C) > (E) OH OH OH OH OH (iii) (D) > (E) > (C) > (B) > (A) (iv) (E) > (D) > (C) > (B) > (A) OCH3 NO2 (C) (D) Assertion Reason Type Questions (1 Mark) NO2 OCH3 In the following questions a statement of assertion (A) (B) (E) followed by a statement of reason is given. Choose the correct answer out of the following choices. (i) Assertion and reason both are correct statements and reason is correct explanation for Assertion. (ii) Assertion and reason both are correct statements but reason is not correct explanation for Assertion. (iii) Assertion is correct statement but reason is wrong statement. (iv) Assertion is wrong statement but reason is correct statement. 4. Assertion: Phenol does not react with sodium bicarbonate solution. Reason : Phenol is not acidic in nature. 5. Assertion: p-Nitrophenol is more acidic than phenol. Reason: Nitro group helps in the stabilisation of the phenoxide ion by dispersal of negative charge due to resonance. Very Short Answer Type Questions (1 Mark) 6. How will you obtain picric acid from phenol? 7. Convert the 2-methylpropanol to 2-methylpropene. 8. How will you convert anisole to phenol? Short Answer Type Questions-I (2 Marks) 9. Write the mechanism for acid dehydration of ethanol to yield ethene. 10. Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring towards electrophilic substitution and (ii) it directs the incoming substitutents towards ortho and para positions in the benzene ring. 11. Describe the following name reactions: (ii) Coupling reaction of phenol (i) Schotten-Baumann reaction 12. Write the reactions and the conditions involved in the conversion of (i) Propene to acetone (ii) Phenol to salicylic acid Short Answer Type Questions-II (3 Marks) 13. Explain the following name reactions with an example: (i) Kolbe’s reaction (ii) Reimer-Tiemann reaction (iii) Williamson ether synthesis 14. Write the resonance structures of phenol and explain why phenol is more acidic than ethanol? Also explain whether p-nitrophenol will be more or less acidic than phenol. 15. Give reasons: (i) Phenol is more acidic than methanol (ii) The C—O—H bond angle in alcohols is slightly less than the tetrahdral angle (109°28¢) (iii) ((CCHH33))33CC——OOHCHa3ndonCHre3aI.ction with HI gives (CH3)3C–I and CH3OH as the main products and not 1. (iv) 2. (ii) Answers 3. (ii) 4. (iii) 5. (i) 262 Chemistry-12
Aldehydes, Ketones 8 and Carboxylic Acids Topics covered 8.1 Aldehydes and Ketones 8.2 Carboxylic Acids C hapter map ALDEHYDES, KETONES AND CARBOXYLIC ACIDS Organic compounds containing C O group Carbonyl Compounds Carboxylic acids Aldehydes and Ketones R HO C O group Aldehydes: H—C—R R¢—C—R O Nomenclature of carboxylic O acids and their derivatives Ketones: R—C—R or Preparation of Carboxylic O acids and their derivatives Nomenclature of Physical and Chemical Aldehydes and Ketones Properties of Carboxylic acids Preparation of Aldehydes Acidity of Carboxylic acids and and Ketones effect of electron withdrawing and electron donating groups on acidity Physical and Chemical Properties of Aldehydes and ketones of carboxylic acids Uses of Aldehydes and ketones Uses of Carboxylic Acids Distinguishing Aldehydes and Ketones Topic 1. Aldehydes and Ketones Introduction • General Formula: • Aldehydes: Aldehydes are the organic compounds having carbonyl group bonded to one hydrogen • Ketones: Ketones are the organic compounds in atom and one alkyl or aryl group. which carbonyl group is attached to two alkyl/aryl groups or both alkyl and aryl groups. 263
O OO • General Formula: (R, R¢ may be alkyl CH2 = CH—C—H H3C—CH2—C—CH2—C—H or aryl group. Also, R and R¢ may be same or Prop-2-enal 3-Oxopentanal different. (Acrolein) CHO CH3—CH—CHO H3C Nomenclature of Aldehydes and Ketones 3-Methylcyclohexanecarbaldehyde OCH3 • Many aldehydes and ketones are known by 2-Methoxypropanal their common names. These common names are generally derived from the organic acids from CHO which they are obtained. OH • In the IUPAC system, the names of aldehydes OHC—CH2—CH—CH2—CHO and ketones are derived by replacing the ending –‘e’ with ‘al’ and ‘one’, respectively of the CHO 2-Hydroxy corresponding hydrocarbons. cyclopentanecarbaldehyde Propane-1, 2, 3-tricarbaldehyde For eg: • Few examples of aromatic aldehydes are: CHO CHO Hydrocarbon Aldehyde CHO CH3—CH2—CH3 O CHO CH3—CH2—C—H Propane Benzene-1, Propanal 2-dicarbaldehyde Benzaldehyde NO2 (Phthalaldehyde) Ketone CHO 4-Nitro benzaldehyde CHO O CHO OH CH3—C—CH3 Br OCH3 2-Hydroxy Propanone 3-Bromo • However, the simplest aromatic aldehyde benzaldehyde OH benzaldehyde (C6H5CHO) is named according to the IUPAC (m-Bromobenzaldehyde) (Salicylaldehyde) system by the common name benzaldehyde 4-Hydroxy-3-methoxy itself and so other derivatives of aromatic aldehydes are named accordingly as derivatives benzaldehyde of benzaldehyde. (Vanillin) • The number of carbonyl groups is named as per the rules by adding the prefix –di, tri, etc if more • Few examples of aliphatic ketones are: than one ‘ C=O’ group is present. O • Few examples of aliphatic aldehydes and ketones are: CH3—C—CH2—CH2—CH3 3-Methyl CH3 CH3 O CH3 OO cyclopentanone O CH3 C H CH3 CH2 CH2 C H CH3—CH—C—CH—CH3 CH3 Ethanal Butanal 2, 4-Dimethylpentan-3-one 2-methylcyclohexanone (Acetaldehyde) (Butyraldehyde) (Disopropyl ketone) O CH3 O O CH3 CH C H CH3—C CH—C—CH3 CH3—CH2—CH—C—CH—CH2—CH3 CH3 4-Methylpent-3-en-2-one CH3 CH3 2-Methylpropanal (Mesityl oxide) 3, 5-Dimethylheptan-3-one (Isobutyraldehyde) (Disec-butyl ketone) Br CH3 O • Few examples of aromatic ketones are: OO CH3—CH2—CH2—CH—CH—CH2—C—H C—CH3 C—CH2—CH3 4-Bromo-3-methylheptanal OO CH3—CH2—CH CH—C—H C—H 1-Phenylethanone 1-Phenylpropanone (Acetophenone) Pent-2-enal Cyclohexanecarbaldehyde 264 Chemistry-12
O O O C—CH3 C CH3(CH2)9 —C—OC2H5 (i) DIBAL-H (ii) H2O O CH3(CH2)9—C—H + C2H5OH • From Hydrocarbons: Benzophenone F ã By oxidation of methyl benzene: (4-Fluorophenyl) ethanone Etard Reaction: Chromyl cfohrlomriadech(CrorOm2iCulm2) oxidises methyl group to (4-Fluoroacetophenone) Preparation of Aldehydes complex, which on hydrolysis gives the • By oxidation of alcohols: Oxidation of primary corresponding benzaldehyde. alcohols in the presence of mild oxidising agents like PCC, CrO3 give aldehydes: CH 3 CS2 + CrO2Cl2 H RCH2OH PCC R—C==O Toluene or CrO3 Aldehyde CH(OCrOHCl2)2 CHO • By dehydrogenation of alcohols: Vapours of + a primary alcohol when passed through heated copper at 573 K forms an aldehyde. H3O Chromium complex Benzaldehyde + H2 Use of chromium oxide e(CcroOn3)v:eTr toeludent eo or sub stituted t oluen • By hydration of alkynes: Ethyne on hydration with benzylidene diacetate in the presence of HgSO4/dil.H2SO4 at 333 K forms acetaldehyde: chromic oxide dissolved in acetic anhydride which on hydrolysis gives benzaldehyde. CH3 + CrO3 + (CH3CO)2O 273–283 K O • By Rosenmund reduction: Hydrogenation O C CH3 CHO of acyl chlorides over palladium catalyst using CH + + 2CH3COOH barium sulphate can form aldehydes: O C CH3 H3O Ethanoic O D (hydrolysis) Benzaldehyde Acid ã By side chain chlorination followed by hydrolysis: Side chain halogenation of toluene form benzal chloride which on hydrolysis can give benzaldehyde. • By reduction of nitriles (Cyanides) CH3 CHCl 2 CHO CI2 H2O ã Stephen Reaction: Reduction of nitriles in the hv 373 K presence of stannous chloride and HCl can form imine, which on hydrolysis gives the (hydrolysis) corresponding aldehyde as follows: Toluene Benzal chloride Benzaldehyde + ã Gatterman-Koch reaction: Benzene and H3O its derivatives on treatment with carbon RCN + SnCl2 + HCl RCH = NH (hydrolysis) RCHO monoxide and HCl in the presence of anhydrous aluminium chloride or cuprous ã Nitriles can be selectively reduced by chloride (CuCl) forms benzaldehyde or DIBAL-H (Diisobutylaluminium hydride) to substituted benzaldehydes as the product. form aldehydes as follows: CHO (i) AlH(i-Bu)2 RCN (ii) H2O R—CHO CO, HCl Anhyd. AlCl3/CuCl (i) AlH(i-Bu)2 CH3—CH=CH—CH2CH2—CN (ii) H2O Toluene Benzaldehyde CH3—CH=CH—CH2CH2—CHO Preparation of Ketones • By oxidation of alcohols: Oxidation of secondary • By reduction of esters: Esters can be reduced alcohols in the presence of oxidising agents like to form aldehydes in the presence of DIBAL-H K2Cr2O7/dil.H2SO4,CrO3 can form ketones: (Diisobutylaluminium hydride): Aldehydes, Ketones And CArboxyliC ACids 265
• By heating calcium salts of acids: • By dehydrogenation of alcohols: When the O Dry O vapours of secondary alcohols are passed over distillation heated copper metal at 573 K, dehydrogenation CH3—C— O CH3—C—CH3 + CaCO3 reaction takes place and a ketone is formed as Ca the product. Acetone Calcium Carbonate CH3—C— O O • By hydration of alkynes: Hydration of alkynes Physical Properties of Aldehydes and Ketones other than acetylene will yield ketones. For • Boiling Point: Due to dipole-dipole interactions example, propyne on hydration using HgSO4/dil. these molecules are associated better than H2SO4 at 333 K forms propanone. comparable hydrocarbons. Hence, they have higher boiling points than corresponding CH3—CºCH + H—OH HgSO4/H2SO4 hydrocarbons but lower than alcohols due to 333 K absence of H-bonding. (hydrolysis) • Solubility: Lower members are soluble in water due to H-bonding with water molecules. CH3—C=CH2 Isomerisation CH3—C—CH3 Chemical Properties of Aldehydes and Ketones O—H O Aldehydes are generally more reactive than ketones Propanone toward nucleophilic addition reactions due to steric and electronic reasons (or inductive effect). • From acyl chlorides: Acyl chlorides on treatment with dialkyl cadmium (prepared by • Electronic Effect: Relative reactivity of the reaction of cadmium chloride with Grignard aldehydes and ketones towards nucleophilic reagent) form ketones: addition reactions is due to the partial positive charge on the carbonyl carbon atom. Greater the 2 R—Mg—X + CdCl2 ———→ R2Cd + 2Mg(X)Cl postive charge on the carbonyl carbon, greater is 2 R¢—C—Cl + R2Cd ———→ 2R¢—C—R + CdCl2 its reactivity. Electron releasing power of the two alkyl groups in ketones is more than one alkyl OO group as there in aldehydes. Therefore, positive • From nitriles: Nitriles on reaction with Grignard charge is reduced in case of ketones as compared to the aldehydes. Thus, ketones are less reactive reagent in ether, followed by hydrolysis can give than aldehydes. ketones: CH3—CH2—C N + C6H5MgBr ether NMgBr O Br • Steric Effect: As the number and size of alkyl H3O+ group increases, the steric hindrance to the CH3CH2—C C2H5—C + Mg attack of nucleophile also increases and the reactivity decreases. In aldehydes, there is only C6H5 C6H5 NH2 one alkyl group and one hydrogen atom, whereas in ketones there are two alkyl groups (same or Propiophenone different). Due to this factor aldehydes are more reactive towards nucleophilic additon reactions (1-Phenylpropanone) over ketones. • By Friedel-Crafts acylation reaction: Benzene or substituted benzene on treatment with acid chlorides in the presence of anhydrous aluminium chloride can form ketones: • Nucleophilic Addition Reactions of Aldehydes and Ketones: ã Addition of hydrogen cyanide (HCN) to form cyanohydrins: – • By ozonolysis of alkenes: C O + :–CN O H+ CN HH H OH CC CH CH3 C = C H + O3 CH3 C Zn/H2O CN OH O Propene Ozone O O Tetrahedral Cyanohydrin O intermediate CH3—C—H + H—C—H + H2O2 ã Addition of sodium hydrogen sulphite (NaHSO3) to form bisulphite addition compound: 266 Chemistry-12
C O + NaHSO3 R'OH, HCl gas OR¢ R¢OH H+ OSO2H OSO2H R–CHO R—CH C C OH proton transfer ONa OH Hemiacetal OR¢ Bisulphite addition R—CH OR¢ + H2O Acetal compound (crystalline) ã Addition of Grignard reagent (RMgX) to form Ketones do not undergo reaction with alcohol: monohydric alcohols. Ketones can react with d– d+ C—O Mg—X H2O ethylene glycol under similar conditions to C O + R—Mg—X R form a cyclic product which is known as Adduct ethylene glycol ketal. C—OH + Mg(OH)X R + H2O ã Addition of alcohols: ã Addition of ammonia and its derivatives to Aldehydes on reaction with monohydric aldehydes: alcohols in the presence of dry HCl gas forms hemiacetal and acetal. R OH R C C O + H2N—Z C N—Z + H2O H H NHZ Z = Alkyl, Aryl, OH, NH2, C6H5NH, NHCONH2 group etc. Z Reagent Name Carbonyl derivative Product Name –H Ammonia C=NH Imine –R Amine C=NR Substituted imine (Schiff’s base) –OH Hydroxylamine C=N–OH Oxime –NH2 Hydrazine C=N–NH2 Hydrazone Phenylhydrazine Phenylhydrazone 2,4-Dinitrophenyl- 2,4 Dinitrophenyl- hydrazine hydrazone O Semicarbazide O Semicarbazone NH C NH2 C=N–NH–C–NH2 • Reduction of Aldehydes and Ketones: R O H2/Ni, Pt or Pd R CH OH ; C LiAlH4 or NaBH4 H ã Reduction to alcohols: Aldehydes and ketones on catalytic hydrogenation (in the H presence of Ni, Pt or Pd metal) or by using saliogtdheiniuutmmcbaoanrloufhmoyrdimnriidupemr(iNmhaayBrdHyr4i)adanesd(tLhseieArceIodHnud4c)ainroygr Aldehyde 1° Alcohol alcohols, respectively. R O H2/Ni, Pt or Pd R CH OH C LiAlH4 or NaBH4 R R Ketone 2° Alcohol ã Reduction to hydrocarbons: Clemmensen reduction: Carbonyl group of aldehydes and ketones can be reduced into Aldehydes, Ketones And CArboxyliC ACids 267
CH2 group on treating with zinc amalgam 2 CH3—CHO dil. NaOH CH3—CH—CH2—CHO D and concentrated hydrochloric acid. Acetaldehyde –H2O (Ethanal) C O Zn–Hg CH2 + H2O OH HCl 3-Hydroxybutanal Wolff-Kishner reduction: Carbonyl group of (Aldol) aldehydes and ketones is reduced to CH2 group on treating with hydrazine followed CH3—CH=CH—CHO But-2-enal by heating with sodium or potassium (Aldol condensation hydroxide in a high boiling solvent such as product) ethylene glycol. CH3 2 CH3—CO—CH3 Ba(OH)2 CH3—C—CH2CO—CH3 D Propanone (Acetone) –H2O C O NH2NH2 C NNH2 KOH/Ethylene glycol CH2 + N2 –H2O heat OH (Ketol) • Oxidation of aldehydes and ketones: 4-Hydroxy-4-methylpentan-2-one ã Aldehydes are oxidised to form carboxylic (Diacetone alcohol) acids in the presence of common oxidising agents such as HNO3, K2Cr2O7, KMnO4, etc CH3 to form carboxylic acids. Even mild oxidising agents like Tollens’ and Fehling’s reagent can CH3—C=CH—CO—CH3 cause oxidation of aldehydes. 4-Methylpent-3-en-2-one ã Ketones can be generally oxidised under drastic (Aldol condensation product) (Mesityl oxide) conditions, i.e. with powerful oxidising agents ã Cross aldol condensation: Aldol like conc. HNO3, KMnO4/H2SO4,K2Cr2O7/ condensation reaction between two different H2SO4 at elevated temperatures. aldehydes and ketones is called cross aldol condensation reaction. If both of these 1 23 [O] carbony compounds contains a-hydrogen R—CH2—C—CH2—R¢ atoms, it gives a mixture of four products: O R—COOH + R¢—CH2COOH + R—CH2COOH + R¢—COOH (By cleavage of C1–C2 bond) (By cleavage of C2–C3 bond) In case of unsymmetrical ketones cleavage occurs in such a manner that keto group remains with the smaller alkyl group. This is known as Popoff’s rule. ã Haloform reaction: Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom i.e. methyl ketones can be oxidised by sodium hypohalite to form sodium salts of the corresponding carboxylic acids having one carbon atom less than that of the carbonyl compound. The methyl group • Canizzaro reaction: Aldehydes which do not can be converted to form haloform. have an a-hydrogen atom can undergo self oxidation and reduction (disproportionation) OO reaction when treated with concentrated alkali R C CH3 NaOX R C ONa + CHX3 (X=Cl, Br, I) to form alcohol and salt of an acid. Haloform H H O + conc. KOH • Reactions of aldehydes and ketones due to H a-hydrogen: C O+ C ã Aldol condensation: Aldehydes and H H ketones having at least one a-hydrogen atom can undergo self condensation reaction in Formaldehyde O the presence of dilute alkali as the catalyst to form a-hydroxy aldehydes (aldol) or H C OH + H C a-hydroxy ketones (ketol), respectively. H OK Methanol Potassium formate 268 Chemistry-12
Ketones cannot form silver mirror and hence 2 CHO + conc. NaOH do not give this test. Benzaldehyde CH2OH + COONa ã Fehling’s test: When an aldehyde is treated with Fehling’s reagent, it forms a reddish Benzyl alcohol Sodium benzoate brown precipitate of cuprous oxide. • Test to distinguish aldehydes and ketones: Fehling’s reagent: Fehling solution A ã Tollens’ test: When an aldehyde is heated (aqueous solution of CuSO4) + Fehling with Tollens’ reagent it can form a silver solution B (alkaline solution of sodium mirror. Tollens’ reagent is ammoniacal potassium tartarate) solution of AgNO3. R—CHO + 2Cu2+ + 5OH– RCOO– + Cu2O + 3H2O RCHO + 2[Ag(NH3)2]+ + 3OH– ———→ Red-brown RCOO– + 2Ag + 2H2O + 4NH3 ppt. Ketones and aromatic aldehydes do not give Fehling’s test. ExErCIsE 8.1 Multiple Choice Questions (MCQs) (1 Mark) (ii) Assertion and reason both are correct statements but reason is not correct explanation of assertion. 1. Name the product formed when acetaldehyde is treated with excess of ethyl alcohol in the presence (iii) Assertion is correct statement but reason is of dry HCl gas. wrong statement. (i) 1,1-Diethoxyethane (iv) Assertion is wrong statement but reason is correct statement. (ii) Propanone (iii) Acetone (iv) 1,2-Diethoxyethane 7. Assertion: Formaldehyde is a planar molecule. Reason: It contains sp2 hybridised carbon atom. 2. Name the product formed when benzene is treated with acetyl chloride in the presence of anhydrous 8. Assertion: Aromatic aldehydes and formaldehyde AlCl3. undergo Cannizzaro reaction. (i) Chlorobenzene (ii) Toluene Reason: Aromatic aldehydes are almost as (iii) Acetone (iv) Acetophenone reactive as formaldehyde. 3. Name the alkene which can only form acetaldehyde 9. Assertion: Benzaldehyde is less reactive than as the product on reductive ozonolysis. ethanal towards nucleophilic attack. (i) Ethene (ii) But-2-ene Reason: All the carbon atoms of benzaldehyde are sp2 hybridisation. (iii) But-1-ene (iv) Propene 4. Name the alkene which on reductive ozonolysis 10. Assertion: Cross canizzaro reaction between gives acetone as the only product. formaldehyde and benzaldehyde gives benzyl alcohol and formate ion. (i) 2,3-Dimethylbut-2-ene (ii) Hex-3-ene (iii) Propene Reason: Formaldehyde is a better hydride donor than benzaldehyde. (iv) 2-Methylbut-2-ene 5. What product is formed when benzophenone is Very Short Answer Type Questions (1 Mark) reduced with Zn-Hg/HCl? 11. Name the products formed when calcium acetate (i) Diphenylmethanol is strongly heated and distilled. (ii) Diphenylmethane 12. Why do butanal and butanol have large difference in their boiling points? (iii) Dicyclohexane (iv) Toulene 6. Write the IUPAC name of the lowest molecular 13. Name the products obtained by the reductive weight aldehyde which undergoes iodoform test. ozonolysis of penta-1, 3-diene. (i) Methanal (ii) Ethanal 14. Draw the structure and give the IUPAC name of an aliphatic aldehyde having 5 carbon atoms (iii) Propanal (iv) Butanal which undergoes Cannizzaro reaction. Assertion-Reason Type Questions (1 Mark) 15. Arrange the following in their increasing order of Note: In the following questions, a statement of reactivity towards HCN: [AI 2012] assertion followed by a statement of reason is given. Choose the correct answer out of the following choices CH3CHO, CH3COCH3, HCHO, C2H5COCH3 on the basis of the above passage. 16. H o w w i l l t h e c o n v e r s i o n a c e t o n e i n t o (i) Assertion and reason both are correct statements 2-methylpropan-2-ol is carried out? and the reason is correct explanation of assertion. 17. How will you be able to convert acetaldehyde into propan-2-ol? Aldehydes, Ketones And CArboxyliC ACids 269
18. How can you convert benzaldehyde into 1-phenyl- (ii) B e n z a l d e h y d e , p - T o l u a l d e h y d e , 1-ethanol? p-Nitrobenzaldehyde, Acetophenone [NCERT] 19. Which type of aldehydes and ketones can undergo aldol condensation reaction? 39. Write a possible explanation for each of the following: 20. Which type of aldehydes can undergo Cannizzaro reaction? (i) Cyclohexanone forms cyanohydrin in good yield but 2.2,6-trimethyl cyclohexanone does 21. What products are formed when calcium formate not. is heated and distilled? (ii) HThoewreevaerreotnwlyo—onNeHis2ignrvooulvpesdininsetmheicfaorrmbaaztiidoen. 22. Write the product when a mixture of calcium of semicarbazones. benzoate and calcium formate are heated and dry distilled. 23. Which reagent is used to distinguish between Short Answer Type Questions-II (3 Marks) pentan-2-one and pentan-3-one? 40. Both C = O and C = C bonds can undergo 24. Which type of reaction and reagents are used for addition reactions. Write about the basic the conversion of acid chlorides to corresponding differences in their nature. aldehydes? 41. Under what circumstances may an aldehyde can 25. Which reagent can be used to distinguish between be prepared by the oxidation of primary alcohols, acetaldehyde and acetone? ROH, using acid dichromate? 26. What product is obtained when benzaldehyde 42. Give the reagent used to bring about the following reacts with aniline? transformations: 27. Aldehydes are more reactive than ketones towards (i) Pent -3-en-2-ol to pent -3-en-2-one nucleophilic reagents. Explain (ii) But-1-yne to Butan-2-one 28. Mention one use of formalin in industry. (iii) p-nitrotoluene to p-nitrobenzaldehyde. 29. Arrange the following compounds in increasing 43. Carry out the following conversions? order of their boiling points: (i) Acetone from ethanol CH3CH2CH2CHO, CH3CH2CH2CH2OH, (ii) Methanal to ethanal (not more than 3 steps) C2H5—O—C2H5, CH3CH2CH2CH2CH3 [NCERT] 30. Arrange the following compounds in increasing (iii) Propanal to propane order of their boiling points: 44. Write the names of the reagents used to bring about the following transformations: CH3CHO,CH3CH2OH,CH3OCH3,CH3CH2CH3 (i) Hexan-l-ol to hexanal [NCERT] (ii) Cyclohexanol to cyclohexanone Short Answer Type Questions-I (2 Marks) (iii) p-fluorotoluene to p-fluorobenzaldehyde 31. Why is it necessary to maintain the pH during the (iv) Ethanenitrile to ethanal reaction of aldehydes and ketones with ammonia derivatives? (v) Allyl alcohol to propenal (vi) But-2-ene to ethanal [NCERT] 32. Explain why sodium bisulphite is used for the 45. Would you expect benzaldehyde to be more purification of aldehydes and ketones? reactive or less reactive towards nucleophilic addition reactions than propanal? Explain your 33. Why do aldehydes and ketones have higher dipole answer. [NCERT] moment values than those of the corresponding alcohols? 46. Draw the structures of the following compounds: 34. Benzophenone does not react with NaHSO3. (i) a-Methoxypropionaldehyde Explain why? (ii) 3-Hydroxybutanal 35. Write the structural formulae and give the IUPAC (iii) 2-Hydroxycyclopentane carbaldehyde names for all the aldehydes and ketones having (iv) 4-Oxopentanal the molecular formula C4H8O. (v) Di-sec butyl ketone 36. What is Tollens’ reagent? Write one use of this (vi) 4-Fluoroacetophenone [NCERT] reagent. [AI 2010] 47. An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular 37. Write Fehling’s solution test used for the mass of the compound is 86. It does not reduce identification of aldehydic group (only equation). Tollens’ reagent but forms an addition compound 38. Arrange the following compounds in increasing with sodium hydrogensulphite and give positive order of their reactivity towards nucleophilic iodoform test. On vigorous oxidation it gives addition reactions: ethanoic and propanoic acid. Write the possible (i) Ethanal, Propanal, Propanone, Butanone structure of the compound. [NCERT] 270 Chemistry-12
Long Answer Type Questions (5 Marks) 52. Write the structural formulae and names of the four possible aldol condensation products 48. Write the structural formulae of the following: that can be obtained by treating propanal with butanal. In each case, indicate which aldehyde (i) 3-Oxopentanal acts as nucleophile and which as an electrophile? [NCERT] (ii) 4-Chloro-2-methyl-3-oxobutanamide 53. Complete the following reactions: (iii) 1-Phenylpentan-1-one (i) CH3CH2CHCl2 Boil, alkali → ? (iv) 4-Chloropentan-2-one (v) 2-hydroxycyclopentane carbaldehyde 49. Write the structures of the products formed in the following reactions: O (ii) ? (i) + C2H5 C Cl Anhyd. AlCl3 CS2 + ------?------ Anhydrous AlCl3 (ii) (C6H5CH2)2Cd + 2CH3COCl→ (iii) O (iii) C CH3 CH3 (iv) (i) CrO2Cl2 [NCERT] + (ii) H3O NO2 (iv) (v) (v) 50. Predict the products of the following reactions: (i) (vi) C6H5CHO H2NCONHNH2→ ? O O2N (vii) R − COCl + H2 Pd−BaSO4 → ? (ii) + NH2—NH NO2 (viii) HC ≡≡ CH + H2O 410%%HHg2SSOO44 → (ix) CH3COCH3 NaIO2H→ (iii) R—CH CH CHO + O (x) CH3CHO + NaHSO3 → O NH2 C NH NH2 H+ 54. An organic compound (A) with molecular formula C8H8O forms an orange-red precipitate with 2,4- C DNP reagent and gives yellow precipitate on (iv) CH3+ CH3CH2NH2 H+ heating with iodine in the presence of sodium hydroxide. It neither reduces Tollens’ or Fehling’s O reagent nor does it decolourise bromine water (v) + C6H5—C—Cl Anhyd. AlCl3 [NCERT] or Baeyer’s reagent. On drastic oxidation with CS2 chromic acid, it gives a carboxylic acid (B) 51. Give the structures of the following compounds: having molecular formula C7H6O2. Identify the compounds (A) and (B) and explain the reactions (i) 3-Methylbutanal involved. [NCERT] (ii) p-Nitropropiophenone 55. What do you mean by the following terms? Give (iii) p-Methylbenzaldehyde an example of the reaction involved in their (iv) 4-Methylpent-3-en-2-one formation in each case: (v) 4-Chloropentan-2-one (i) Cyanohydrin (ii) Acetal (vi) 3-Bromo-4-phenylpentanoic acid (iii) Semicarbazone (iv) Aldol (vii) p, p′–Dihydroxybenzophenone (v) Hemiacetal (vi) Oxime (viii) Hex-2-en-4-ynoic acid [NCERT] (vii) Ketal (viii) Imine (ix) a-Methoxypropionaldehyde (ix) 2,4-DNP-derivative (x) 4-oxopentanal (x) Schiff’s base [NCERT] Aldehydes, Ketones And CArboxyliC ACids 271
56. Name the following compounds according to (i) Propanal and propanone IUPAC system of nomenclature: (ii) Acetophenone and benzophenone (i) CH3CH(CH3)CH2CH2CHO (iii) Phenol and benzoic acid (ii) CH3CH2COCH(C2H5)CH2CH2Cl (iv) Benzoic acid any ethyl benzoate (iii) CH3CH CHCHO (v) Pentan-2-one and pentan-3-one (iv) CH3COCH2COCH3 (vi) Benzaldehyde and acetophenone (v) OHC—C6H4CHO—p [NCERT] (vii) Ethanal and propanal [NCERT] 57. Write the IUPAC names of the following ketones 62. How will you bring about the following conversions and aldehydes. Wherever possible, also give their in not more than two steps? common names. (i) Propanone to propene (i) CH3CO(CH2)4CH3 (ii) Benzoic acid to benzaldehyde (ii) CH3CH2CHBrCH2CH(CH3)CHO (iii) Ph—CH CH—CHO (iii) Ethanol to 3-hydroxybutanal (iv) Benzene to m-nitroacetophenone CHO (v) Benzaldehyde to benzophenone (iv) (v) PhCOPh [NCERT] (vi) Bromobenzene to 1-phenylethanol (vii) Benzaldehyde to 3-phenylpropan-1-ol 58. Draw the structures of the following derivatives (viii) Benzaldehyde to a-hydroxyphenylacetic acid of aldehydes and ketones: (ix) Benzoic acid to m-nitrobenzyl alcohol (i) T h e 2 , 4 - d i n i t r o p h e n y l h y d r a z o n e o f [NCERT] benzaldehyde 63. Complete each synthesis by giving missing (ii) Cyclopropanone oxime starting material, reagent or products. (iii) Acetaldehydedimethylacetal CH2CH3 (iv) The semicarbazone of cyclobutanone (i) KMnO4 KOH, heat (v) The ethylene ketal of hexan-3-one (vi) The methyl hemiacetal of formaldehyde (ii) ? (i) O3 2 O [NCERT] (ii) Zn/H2O 59. Predict what products are formed when (iii) C6H5CHO H2NCONHNH2 cyclohexane carbaldehyde reacts with each of O the following reagents: (i) PhMgBr and then H3O+ C (ii) Tollens’ reagent (iv) (iii) Semicarbazide and weak acid (iv) Excess ethanol and acid O (v) Zinc amalgam and dilute hydrochloric acid (v) + [NCERT] [Ag(NH3)2] [NCERT] 60. Which of the following compounds would undergo aldol condensation, which the Cannizzaro reaction CHO and which neither? Write the structures of the 64. Complete each synthesis by giving missing starting material, reagent or products. expected products of aldol condensation and CHO Cannizzaro reaction. (i) NaCN/HCl (i) Methanal [CBSE 2022] COOH (ii) 2-Methylpentanal (ii) (iii) Benzaldehyde (iv) Benzophenone (v) Cyclohexanone [NEET 2017] (iii) CH3COCH2COOC2H5 (i) NaBH4 (vi) 1-Phenylpropanone + (ii) H (vii) Phenylacetaldehyde (iv) OH CrO3 (viii) Butan-1-ol (ix) 2, 2-Dimethylbutanal [NCERT] 61. Give simple chemical tests to distinguish between (v) CH2 ? CHO [NCERT] the following pair of compounds. 272 Chemistry-12
Answers 8.1 1. (i) 2. (iv) 3. (ii) 26. Benzalaniline (C6H5CH=NC6H5) or Schiffs base is obtained. 4. (i) 5. (ii) 6. (ii) 7. (i) 8. (iii) 9. (ii) 27. Due to electron repelling, +I effect of two alkyl 10. (i) groups attached to C = O group in ketones partial 11. CH3COO positive charge on carbonyl carbon decreases as CH3 compared to that of aldehydes which have only one CH3COO Ca Dry distillation alkyl/aryl group. Thus, ketones are less reactive. ∆ C = O + CaCO3 CH3 28. In the preparation of phenol-formaldehyde Acetone resin (Bakelite) and also used as a solvent for 12. Butanol molecules are linked together by strong preserving biological specimens. hydrogen bonds, as a result of which its boiling point is more than that of butanal. 29. The molecular masses of these compounds are similar i.e., in the range of 72-74. 13. H2C = CH – CH = CH – CH3 (i) O3/CH2Cl2 (ii) Zn/H2O Since, only butan-1-ol can undergo extensive Penta-1,3-diene intermolecular H-bonding, therefore its boiling HCHO + OHC—CHO + CH3CHO point is the highest. Butanal is more polar than Formaldehyde Glyoxal Acetaldehyde ethoxyethane, therefore dipole-dipole interactions 14. (CH3)3 C–CHO → 2, 2-Dimethylpropanal in butanal is stronger than that in ethoxyethane. Only van der Waals forces of attraction exist 15. C2H5COCH3 < CH3COCH3 < CH3CHO < HCHO between molecules of n-pentane. Hence, boiling 16. By treating acetone with excess oafnCpHr3eMpgaBrre, fol lowed b y hydr olysi s we c point n-pentane is lowest. Thus, the overall order of increasing boiling point is: 2-methylpropan-2-ol from acetone: CH3CH2CH2CH2CH3 < C2H5—O—C2H5 OH < CH3CH2CH2CHO < CH3CH2CH2OH CH2—C—CH3 + CH3MgBr H+ CH3—C—CH3 30. CH3CH2CH3 < CH3OCH3 < CH3CHO O (in excess) (hydrolysis) < CH3CH2OH CH3 The above order can be explained on the nature 2-Methylpropan-2-ol 17. By htryedartoilnygsiascewtealcdaenhypdreepwairtehpCrHop3aMng-B2-ro,lf.ollowed of intermolecular forces existing in between by tinhteesremmoloelceuculalresH. -Ebothnadninogl ,(wChHi3cChHis2OthHe)stinrovnoglveesst followed by Ethanal molecules which has higher dipole-dipole interactions than methoxymethane, which are slightly polar and only van der Waals forces exists between propane molecules, which 18. bByyhtryedartoilnygsibsewnezacladnehpryedpeawreit1h-pChHe3nMylg-I1,-feotlhloawnoeld. has the least strength. CHO H+ CH—CH3 31. tTohealaddedhityidoensofaanmdmkoentoiandeseriisvaatlivweasy(sNHdo2n–geroinupa) + CH3MgI (hydrolysis) OH weakly acidic medium (pH~3.5). If the medium is 1-Phenyl-1-ethanol strongly acidic, then the ammonia derivative will 19. Aldehydes and ketones which contains a-hydrogen also gets protonated and it will not be able to act atom can undergo aldol condensation. as a nucleophile. Also, if the medium is basic then base may attack carbonyl carbon and interfere in 20. Aliphatic and aromatic aldehydes which do not the reaction. contain a-hydrogen atoms can undergo cannizaro reaction. 32. Aldehydes and ketones will react with sodium bisulphite to form the addition compound: 21. Formaldehyde is formed as the product. 22. Benzaldehyde is the main product formed. The addition products so formed are crystalline 23. obI2nu/Net hanOaovHsiunicgshCthgHer3orCueOapg-egexrnoitsut(psIogidnivopefosernymetaltlneo-ws3t)-p.opPntee.notfthaCunHs-2Iit-3 solids. These can be decomposed by using mineral acids or aqueous alkalies to form back the original does not give this reaction. aldehydes and ketones. Therefore, this reaction can be used for the purification of aldehydes and 24. asRudopdspeitnoiormtneudonfdos’nsulrpBehaduSurOcto4ir,onpq,uaHrint2ioailnlilnyteh.peopisroenseendcebyoftPhde ketones. 25. Tollens’ reagent or Fehling’s solution Aldehydes, Ketones And CArboxyliC ACids 273
33. The carbonyl group in aldehydes and ketones Due to resonance the electron density on this contains a double bond (one sigma and one NH2 group decreases and hence it does not p-bond) between carbon and oxygen atoms. Since, act as a nucleophile. In contrast, the lone oxygen is more electronegative than carbon, the pair of electrons on the other—NH2 group p electrons get shifted to the oxygen atom to give (i.e. the one attached to NH) is not involed complete charge separation due to resonance as in resonance and is therefore available for follows: nucleophilic attack on the C O group of aldehydes and ketones. δ+ δ– +– 40. The C = O group undergoes nucleophilic addition, C=O C—O while C = C undergoes only electrophilic addition reactions. This difference is due to the fact On the other hands the s-electrons of C–O bond that C-atom of C = O group is more electrophilic in alcohols are tightly bonded. Consequently, the than the C-atom of C = C group, since magnitude of (+ve) and (–ve) charges developed is C = O group has polar C-O bond, because oxygen is lower in alcohols. As a result, the dipole moment more electronegative than carbon. Thus, carbon atom values of aldehydes and ketones (2.3–2.8 D) of C = O group easily reacts with nucleophiles. The is higher than that of corresponding alcohols C = C group is nucleophilic due to p-electrons (1.6–1.8 D). and hence reacts with electrophiles only. 34. apThthteeanacykdldoigtfrioo(nuHpoSsfONc3aa–)nHiSoaOnct.3 involves the nucleophilic 41. If the aldehyde product is more volatile than the In benzophenone, two reactants, i.e. alcohol and H2O, then it may be as a hindrance for the removed from the reaction mixture by distillation attacking nucleophile. Therefore, benzophenone process, as soon as it is formed. For example, does not react with NaHSO3. acetaldehyde (b.pt. 294 K) can be prepared from 35. Aldehydes: ethyl alcohol (b.pt. 351 K) by this method. CH3CH2CH2CHO; 42. (i) PCC (C5H5 N·CrO3·HCl in CH2Cl2) Butanal (ii) Dilute H2SO4–HgSO4 at 333 K (iii) CrO3 in the presence of (CH3CO)2O followed Ketones: by hydrolysis. 36. BAomthmoanliipahcaaltiscilvaenrdniatrroamteastoicluatilodneh[Aygd(eNsHre3)d2]uOcHes. 43. (i) CH3CH2OH [O] CH3COOH Ca(OH)2 Tollens’ reagent to give metallic silver and thus used K2Cr2O7/H+ as a test for aldehydes. Ethanol Acetic acid 37. RCHO + 2Cu(OH)2 + NaOH (CH3COO)2Ca Heat CH3COCH3 ∆ Aldehyde Calcium acetate Acetone H2O R—COONa + Cu2O + 3H2O (ii) HCHO CH3MgBr CH3CH2OMgBr (Hydrolysis) Red ppt. (Cuprous oxide) 38. (i) Butanone < Propanone < Propanal < Ethanal Methanal Addition product (ii) A c e t o p h e n o n e < p - T o l u a l d e h y d e < CH3CH2OH [O] CH3CHO Benzaldehyde < p-Nitrobenzaldehyde Ethyl alcohol PCC Ethanal 39. (i) This occurs because of the presence of three (iii) CH3CH2CHO NH2NH2 methyl groups at a-position with respect to C O group, the nucleophile attack Propanal by the CN– ion does not occur due to steric KOH/glycol CH3CH2CH NNH2 473 K CH3CH2CH3 + N2 Addition product Propane hindrance. However, there is no such steric 44. (i) C5H5NH+CrO3Cl–(PCC) in CH2Cl2 hindrance in case of cyclohexanone. (ii) K2Cr2O7/H2SO4 (iii) CrO3/(CH3CO)2O followed by H3O+, heat (D) (ii) Semicarbazide hisasditrwecot—lyNaHtt2acghreoduptso but (iv) Diisobutyl aluminium hydride (DIBAL-H) one of it which the C O group is involved in resonance, as shown below: followed by hydrolysis O (v) C5H5—NH+CrO3Cl–(PCC) in CH2Cl2 H2N C N HNH2 O– (vi) O3/ Zn dust, followed by H2O 45. O O– + C NHNH2 CH3 CH2 C H CH3 CH2 CH H2N O– Propanal + + Due to weaker +I effect of the ethyl group in H2N C NHNH2 propanal, the positive charge on the carbon atom 274 Chemistry-12
of the carbonyl group is only reduced to a small therefore it must be a methyl ketone and its extent. s(Ptreuncttaunra-2l -foonrme)u. lTahweoureldacbteioCnHs 3aCrOeCiHllu2CsHtr2aCtHed3 below: O O O C C+ C O CH3 SO–3 Na+ H H H Benzaldehyde ++ CH3 C CH2CH2CH3 + NaHSO3 C Pentan-2-one CH3CH2CH2 OH O O O (C5H10O) C C + C H +3I2 + 4NaOH CHI3 + CH3CH2CH2COONa H H Iodoform Sodium butanoate In contrast, in benzaldehyde the positive charge [O] CH3COOH + CH3CH2COOH on the carbonyl carbon atom is reduced to a far (K2Cr2O7/conc. H2SO4) Ethanoic acid Propanoic acid greater extent due to stronger +R effect of the benzene ring. As a result of it, the carbon atom of O carbonyl group in benzaldehyde is comparatively less electrophilic than the carbon atom of the 48. (i) CH3CH2—C—CH2CHO carbonyl group of propanal. The polarity of the Cl O CH3 O carbonyl group is also reduced in benzaldehyde due to resonance effect and hence, benzaldehyde is (ii) CH2—C—CH— C—NH2 less reactive than propanal towards nucleophilic O addition reactions. (iii) C6H5—C—CH2CH2CH2CH3 Cl O 46. (i) (iv) CH3—CH—CH2—C—CH3 O (v) 4 321 O (ii) CH3 CH CH2 C H 49. (i) + C2H5 C Cl Anhyd. AlCl3 CS2 OH Propanoyl chloride (iii) Benzene O (iv) 5 43 O H C C2H5 + HCl CH3 C CH2 21 O Ethylphenyl ketone CH2 C (Propiophenone) O O (ii) (C6H5CH2)2 Cd + 2CH3 C Cl Dry ether (v) CH3 CH2 CH C CH CH2 CH3 Dibenzyl- Ethanoyl CH3 CH3 cadmium chloride O (vi) 2CH3 C CH2C6H5 + CdCl2 Benzylmethyl ketone 47. TSihnecme,oltehceulgairvfeonrmcuomlapoof uthnedcofomrpmosunadnisaCd5dHit1i0oOn. (iii) CH3 C C—H + HOH Hg2+, dil. H2SO4 product with NaHSO3, therefore, it must be a carbonyl compound, either an aldehyde or a Propyne ketone. However, it does not reduce Tollens’ reagent, therefore it cannot be an aldehyde. OH Tautomerises O Since the compound gives positive iodoform test, CH3 C CH2 CH3 C CH3 Propanone Adduct Aldehydes, Ketones And CArboxyliC ACids 275
(iv) CH3 2CrO2Cl2 (vii) CS2 O2N p-Nitrotoluene (Etard reaction) OCrCl2OH H3O+ (viii) 6 5 4 3 2 1 CH (hydrolysis) CH3 C C CH CH COOH OCrCl2OH O2N (ix) CH3— CH—CHO OCH3 (x) CH3—C—CH2—CH2—CHO O2N CHO O p-Nitrobenzaldehyde 52. (i) H (v) CH3CH2CH2CH2CH2CH2OH CrO3 CH3CH2CHO + CH3—CH—CHO OH– (Aldol CH3CH2CH2CH2CH2CHO Propanal Propanal condensation) (Electrophile) (Nucleophile) 54 3 21 CH3CH2 CH CH CHO NOH 50. (i) OH CH3 ON NO 3-Hydroxy-2-methylpentanal 2 2 In this reaction, propanal acts both as an NNH electrophile as well as a nucleophile. (ii) H (ii) O CH3CH2CHO + HC CHO – (iii) R CH CH CH N NH C NH2 OH CH3 Propanal (iv) C NCH2CH3 (Electrophile) CH2CH3 Butanal (Nucleophile) 543 2 1 CH3CH2CH CH CHO (v) OH CH2CH3 O 2-Ethyl-3-hydroxypentanal 51. (i) CH3 CH—CH2—C—H CH3 Here, propanal acts as an electrophile and butanal as a nucleophile. (ii) (iii) H CH3CH2CH2CHO + HC CHO – Butanal α OH (Electrophile) CH3 Propanal (Nucleophile) 6543 2 1 CH3CH2CH2CH CH CHO (iii) OH CH3 3-Hydroxy-2-methylhexanal (iv) 5 43 2 1 In this case, butanal acts as an electrophile CH3 C CH C CH3 and propanal as a nucleophile. (iv) H CH3 O CH3CH2CH2CHO + HC CHO – OH (v) Butanal CH2CH3 (Electrophile) Butanal (Nucleophile) (vi) 5 43 2 1 6543 2 1 CH3 CH CH CH2 COOH CH3CH2CH2CH CH CHO C6H5 Br OH CH2CH3 2-Ethyl-3-hydroxyhexanal 276 Chemistry-12
Now, here butanal acts both as an electrophile (iii) as well as a nucleophile. (iv) 53. (i) (ii) (v) CH2 + HBr Peroxide CH2Br NaOH CH2OH Cu/ CHO 300°C 1 B2H6 CH2OH oxidation 2 H2O2/OH– [O] O molecular formula, R2C(OR¢)2, in which R and R¢ are the alkyl/aryl group. For eg. (vi) C6H5—CH==N—NH—C—NH2 (vii) R—CHO (viii) CH3—CHO CH3CH2CHO CH3OH OCH3 (ix) CHI3 + CH3COONa HCl gas CH3CH2CH (x) CH3CH(OH)OSO2Na OH 54. On treatment of (A) with 2,4-DNP, it forms a DNP- Hemiacetal derivative, thus it is confirmed that it contains CH3OH OCH3 H+ a carbonyl group. Since (A) does not reduce CH3CH2CH + H2O Tollen’s reagent, so it must be a ketone. It does Acetal OCH3 not decolourise bromine water or Bayer’s reagent (iii) Semicarbazone: It is a derivative of carbonyl compounds or imines formed by the means unsaturation is due to aromatic ring. condensation reaction between aldehydes or (A) is phenyl methyl ketone, which undergoes oxidation reaction in the presence of H2CrO4, ketones and semicarbazide. For eg. which acts as an oxidising agent to form (B), i.e. Benzoic acid. CH3CHO + NH2NH − C − NH2 → O O CH3C = NNH − C − NH2 C O2N CH3+ H2N—NH O NO2 –H2O (iv) Aldol: Aldehydes having at least one a-H (A) (C8H8O) 2,4-DNP atom can undergo condensation reaction in the presence of aqueous alkali, and forms CH3 O2N an intermediate product (which later loses a water (H2O) molecule to form another class C N NH NO2 of aldehyde) called aldol. For eg. 2,4-DNP derivative 2CH3CHO dil.NaOH CH3—CH—CH2CHO ∆ –H2O OO OH C OH H2CrO4 C CH3 I2/NaOH 2-hydroxy butanal (Aldol) (B) Benzoic acid (A) Acetophenone CH3CH==CHCHO But-2-en-al O (v) Hemiacetal: Hemiacetal are the group of C ONa organic compounds which can be derived + CHI3 through addition reaction between an aldehyde and alcohol. For eg. Yellow ppt CH3—C O +H+ + CH3CH2OH –H+ 55. (i) Cyanohydrin: The product obtained as a result of reaction between the carbonyl H OH compounds, i.e. aldehydes and ketones with hydrogen cyanide is called cyanohydrin. For eg. OCH2CH3 CH3CHO + HCN → CH3CH(OH)CN CH3 H (ii) Acetal: An acetal is a functional group (vi) Oxime: Oximes are a class of organic in organic compounds having the general compounds, which have the general formula: RR¢C=N–OH, where R is an alkyl group and Aldehydes, Ketones And CArboxyliC ACids 277
R¢ may be hydrogen or an alkyl/aryl group. (ix) 2,4-DNP Derivative: These are the They are derived by the reaction between derivatives of carbonyl compounds obtained by the reaction of 2,4-Dinitrophenyl hydrazine carbonyl compounds, i.e. aldehydes and with carbonyl compounds. For eg. ketones with hydroxylamine. For eg. NO2 (vii) Ketal: A ketal is a functional group in C6H5CHO + NH2—NH NO2 ® organic compounds derived from ketones by NO2 acetylation reaction, in which the carbonyl, C6H5—C=N—NH NO2 C=O group is replaced with alkoxy group. For eg. CH3 C2H5OH CH3 OH C2H5OH (x) Schiff’s Base: It is a class of imines having H+ C H+ general formula, RC=NR¢. For eg. C=O (–H2O) ∆ CH3 CH3 OC2H5 CH3COCH3 + CH3NH2 –H2O CH3—C == NCH3 Intermediate CH3 (Hemiketal) 56. (i) 4-Methylpentanal CH3 OC2H5 (ii) 6-Chloro-4-ethylhexan-3-one (iii) But-2-en-l-al C (iv) Pentan-2,4-dione (v) Benzene-1,4-dicarbaldehyde CH3 OC2H5 (viii) Imine: It is the class of organic compounds which can be obtained by the reaction of NH3 with aldehydes and ketones. For eg. 57. IUPAC name Common name (i) Heptan-2-one Methyl n-pentyl ketone (ii) 4-Bromo-2-methylhexanal g-Bromo-a-methyl caproaldehyde b-Phenyl acrolein (iii) 3-Phenylprop-2-enal — (iv) Cyclopentane carbaldehyde Diphenyl ketone (Benzophenone) (v) Diphenyl methanone 58. (i) 59. (i) O (ii) C OH NOH (iii) CH3CH OCH3 O OCH3 (ii) (iii) CH NNH C NH2 O OC2H5 (iv) N NH C NH2 (iv) C OC2H5 (v) CH3 (v) H (vi) H—C OH 60. (a) (ii) 2-Methylpentanal, (v) Cyclohexanone, H OCH3 (vi) 1-Phenylpropanone and (vii) phenyl acetaldehyde have one or more a-hydrogen atoms and hence undergoes aldol condensation reaction. For example, 278 Chemistry-12
CH3 (ii) 2CH3CH2CH2 CH CHO dil. NaOH 76 5 4 32 CH3 CH3CH2CH2 CH CH C CH2CH2CH3 2-Methylpentanal 1 CH3 OH CHO 3-Hydroxy-2,4-dimethyl-2-propylheptanal (v) dil. NaOH 1′ H+ cyclohexan-1-one Cyclohexylidene cyclohexanone CH3 OH CH3 (vi) C O + H—C C dil. NaOH 32 1 C CH C CH2CH3 HO 45 1-Phenylpropanone CH2CH3 O 3-Hydroxy-2-methyl-1,3-diphenylpentan-1-one (vii) CHO dil. NaOH 4 1 CH2—CH = O + H—C CH2 CHO 32 CH CH H OH Phenylacetaldehyde 3-Hydroxy-2,4-diphenylbutanal (b) (i) Methanal, (iii) benzaldehyde and (ix) 2,2-dimethylbutanal does not contain a-hydrogen atom and hence undergoes Cannizzaro reaction. For example, (i) (iii) (ix) (c) (iv) Benzophenone is a ketone having no C6H5COCH3 + 3I2 + 4NaOH a-hydrogen atom, while (viii) Butan-1-ol is an Acetophenone alcohol. Both of these neither undergoes aldol condensation reaction nor Cannizzaro reaction. CHI3 + C6H5COONa + 3NaI + 3H2O Iodoform 61. (i) Propanal responds to the following tests while propanone does not give any of them: (iii) (a) Phenol forms violet coloured complex when treated waictihdngeiuvtersalbFueffClc3oslooluurteidonp, pwth. iolef (a) Propanal + Schiff’s reagent solution → benzoic Pink colour ferric benzoate. (b) Propanal + Tollens’ reagent → Silver (b) Benzoic acid decomposes wNiatHh CevOo3lsuotliuotnioonf mirror and gives effervescence aCwnOitdh2 CgNaOas2HwgCahOsil3iestopnhporetonedovulocilesvaenndo.yt able to react (c) Propanal + Fehling’s solution → Red effervescence precipitate O (iv) (a) peBtovreoonedlvvzuooeclidvce.eaacnCiydOed2fefbecurotvmeepstcohesynelscbeNeanaszHCoCaOtO2e3gdasooseliusstnniooontt (ii) Acetophenone contains (CH3—C—) group and (b) Ethyl benzoate on boiling with excess hence gives iodoform test while benzophenone of NaOH gives ethyl alcohol, which on (C6H5COC6H5) does not give this test. heating with iodine gives a yellow ppt. of Aldehydes, Ketones And CArboxyliC ACids 279
iodoform. On the other hand, benzoic acid CHO OH O does not react to give iodoform test. CH—C6H5 C—C6H5 (v) Pentan-2-one having an acetyl group, i.e. (i) C6H5MgBr Cu O (ii) H2O/H+ 573 K —iodCof—orCmHw3 iftohrmans a yellow coloured ppt. of (v) alkaline solution of iodine (vi) C6H5Br Mg, Dry ether (i) CH3CHO (i.e. iodoform test) while pentan-3-one does C6H5MgBr (ii) H3O+ Bromobenzene not give this test. Phenyl magnesium (vi) (a) Benzaldehyde reduces Tollens’ reagent to give silver mirror test while acetophenone Bromide does not give this test. C6H5 CH CH3 (b) Acetophenone gives iodoform test but OH benzaldehyde does not react to give 1-Phenylethanol iodoform test. CHO (vii) Ethanal gives positive iodoform test nwoitthgivI2e/ NaOH or NaOI, while propanal does (vii) (i) dil. NaOH this test. + CH3CHO (cross aldol condensation) O (ii) H+, heat 62. (i) CH3 NaBH4, CH3OH Benzaldehyde (Reduction) C CH3 CH CHCHO CH2CH2CH2OH OH CH3 CH CH3 conc. H2SO4 H2/Ni Propan-2-ol Heat, (–H2O) (Reduction) CH3CH CH2 3-Phenylprop-2-enal 3-Phenylpropan-1-ol Propene (Cinnamaldehyde) COOH CHO (viii) C6H5CHO NaCN, HCl C6H5 CH CN H2O (Hydrolysis) (ii) NaOH (CO + HCl) OH CaO, heat anhyd. AlCl3 Benzaldehyde Benzoic acid Benzene Benzaldehyde cyanohydrin COOH or CHO C6H5 CH COOH COCl OH SOCl2 H2/Pd + BaSO4 + S a-Hydroxyphenylacetic acid (Mandelic acid) (optically active) (–SO2, (Rosenmund –HCl) reduction) COOH CH2OH CH2OH Benzoyl Benzaldehyde chloride (ix) (i) LiAlH4 conc. HNO3 (iii) Cu, 573 K CH3CHO dil. NaOH (ii) H2O conc. H2SO4, D CH3CH2OH Ethanol NO2 Ethanol or (Aldol Benzoic acid m-Nitro- PCC in CH2Cl2 condensation) CH3 CH CH2CHO benzyl alcohol OH 63. (i) CH2CH3 COOK 3-Hydroxybutanal KMnO4 + CO2 + H2O KOH, heat COCH3 Ethyl benzene Potassium benzoate (iv) (CH3CO)2O conc. HNO3 Anhyd. AlCl3 conc. H2SO4 (ii) (i) O3 2 O (Friedel Crafts reaction) (Nitration) (ii) Zn-H2O Benzene Acetophenone COCH3 Cyclohexylidene Cyclohexanone cyclohexane NO2 (iii) C6H5CHO + H2NHNCONH2 m-Nitroacetophenone Benzaldehyde Semicarbazide Chemistry-12 C6H5CH==NNHCONH2 Benzaldehyde semicarbazone 280
COCl O (iv) + AlCl3 (anhyd.) (iii) 4 3 21 (i) NaBH4 Friedel Crafts reaction + CH3 C CH2COOC2H5 (ii) H Ethyl-3-oxobutanoate Benzene Benzoyl O chloride C OH + HCl 4 3 21 CH3 CH CH2COOC2H5 Ethyl 3-hydroxybutanoate O O Benzophenone (iv) (v) + O – + Ag ¯ C—O [Ag(NH3)2] OH CHO CHO CH—CN (v) CH2 B2H6/THF H2O2 NaOH 64. (i) NaCN/HCl Methylene CH2 B cyclohexane (HCN) COOH 3 COOH 2-Formylbenzoic 2(1'-Hydroxy cyanomethyl) CH2OH PCC acid benzoic acid CH3 (ii) C6H5CH O + H2C CHO dil. NaOH Cyclohexyl methanol (Claisen-Schmidt reaction) Benzaldehyde Propanal CH3 CHO 3 21 Cyclohexane carbaldehyde C6H5CH C CHO 2-Methyl-3-phenylprop-2-en-1-al Topic 2. Carboxylic Acids • However, according to the IUPAC system, the aliphatic carboxylic acids are named by replacing Introduction –‘e’ of the corresponding alkane with —oic acid. • Carboxylic acids are the compounds which contain the carboxyl functional group (—COOH). • The simplest aromatic carboxylic acid is named as ‘Benzoic acid’ according to the IUPAC norms • General Formula: and its derivatives are named accordingly. Nomenclature • The number of carboxyl groups present in a given • Many of the carboxylic acids are known by their organic compound are indicated by adding the common names. prefix –di, tri, etc., if more than one ‘—COOH’ group is present. • IUPAC naming of Carboxylic acid and its derivatives: OO O O O H C OH CH3 C OH CH3CH2 C OH CH3CH2CH2 C OH CH3—CH— C OH Formic acid Acetic acid Propionic acid Butyric acid CH3 (Methanoic acid) Ethanoic acid (Propanoic acid) (Butanoic acid) Iso butyric acid (2-Methylpropanoic acid) COOH COOH CH2COOH CH2COOH CH2CH2COOH CH2 CH2 CH2COOH CH2CH2COOH COOH COOH CH2COOH Succinic acid Adipic acid Oxalic acid Malonic acid Butane-1, 4-dioic acid Glutaric acid (Hexane-1, 6-dioic acid) (Pentane-1, 5-dioic acid) (Ethane-1, 2-dioic acid) Propane-1, 3-dioic acid Br HOOC—CH2—CH—CH2—COOH CH3—CH = CH—COOH CH3—CH—COOH COOH But-2-enoic acid 2-Bromopropanoic acid (Propane-1, 2, 3-tricarboxylic acid) Aldehydes, Ketones And CArboxyliC ACids 281
COOH OH O O CH3—CH—COOH CH3—C—CH2—C—OH H2NCH2COOH Lactic acid 3-Oxobutanoic acid Glycine 2-Hydroxypropanoic acid 2-Aminoethanoic acid Benzoic acid CH2COOH COOH NO2 PhCH2CH2COOH COOH 3-Phenylpropanoic COOH acid NO2 NO2 Phthalic acid Phenyl acetic acid (Benzene 1, 2, 4, 6-Trinitro (2-Phenylethanoic acid) 2-dicarboxylic acid) benzoic acid OO O CH3 CH3—C—Cl C2H5—C—Cl C6H5–C—Cl CH3—C CH—COOH Acetyl Chloride (Propanoyl Chloride) Benzoyl Chloride 3-Methyl (Ethanoyl Chloride) but-2-enoic acid OO C—NH2 C—NH2 OO O H—C—NH2 CH3—C—NH2 CH3CH2—C—NH2 Methanamide Ethanamide Propanamide Benzamide Cyclohexane carboxamide OO OO CONH2 C CH3—C C6H5—C H—C NH O O O Benzene-1, CONH2 2-dicarboxamide C CH3—C C6H5—C CH3—C O O O O Acetic anhydride Benzoic Acetic formic Phthalimide (Ethanoic anhydride) anhydride anhydride COOCH3 O O CH3COOCH3 C6H5—C—O C2H5 H3C—C C—CH CH—C—OH Methyl ethanoate Ethyl ethanoate Methyl benzoate Hex-2-en-4-ynoic acid Preparation of Carboxylic Acids RCHO + 2[Ag(NH3)2]+ + 3OH • From alcohols: Primary alcohols can be readily R–CHO + 2Cu2+ + 5OH– RCOO + 2Ag + 2H2O + 4NH3 oxidised to form carboxylic acids using strong RCOO + Cu2O ¯ + 3H2O Brick red oxidising agents such as potassium permanganate ppt. (KMnO4) in neutral, acidic or alkaline media or • From alkylbenzenes: Aromatic carboxylic by using potassium dichromate (K2Cr2O7) and acids can be prepared by vigorous oxidation of chromium trioxide (CrO3) in acidic media: alkylbenzene using chromic acid or acidic or alkaline potassium permanganate solution as RCH2OH (i) alkaline KMnO4 RCOOH follows: + (ii) H3O RCH2OH CrO3–H2SO4 RCOOH R COOK COOH + • From aldehydes: Aldehydes can be oxidised KMnO4–KOH H3O in the presence of mild oxidising agents like Heat Tollens’ reagent (ammoniacal solution of AgNO3) or Fehling reagent–(Fehling solution A-aqueous Benzoic acid solution of CuSO4) + (Fehling solution B-alkaline solution of sodium potassium tartarate) and they R is an alkyl group, eg. —CH3, —CH2CH3, — will give carboxylic acids: CH2CH2CH3, etc. • From alkenes: Substituted alkenes can be oxidised to form carboxylic acids. On oxidation 282 Chemistry-12
with acidic potassium permanganate or acidic • Boiling point: Carboxylic acids have higher potassium dichromate, alkenes form carboxylic boiling point than the coresponding aldehydes, acid as follows: ketones and even alcohols of comparable molecular masses. This is because of the extensive • From Nitriles: Nitriles when undergo hydrolysis association of carboxylic acid molecules through in the presence of dilute acids or bases form intermolecular hydrogen bonding. amide, which on further hydrolysis can form carboxylic acid. O HO RC CR OH O dimer Chemical Properties of carboxylic acids • From Grignard reagents: Grignard reagent • Acidity of carboxylic acids: Carboxylic acids when reacts with carbon dioxide (dry ice) form are more acidic than phenols. Strength of acid salt of carboxylic acid, which on further hydrolysis depends upon the extent of ionisation, which in forms carboxylic acid. turn further depends upon the stability of the anion formed. R–Mg–X + O=C=O Dry ether O H3O+ RCOOH R—C ã Effect of electron donating substituents on the (hydrolysis) acidity of carboxylic acids: Electron donating substitutents decreases the stability of OMgX carboxylate ion by intensifying the negative charge and hence decreases the acidic • From acyl halides and anhydrides: Acid strength of carboxylic acids. chlorides when hydrolysed with water will give carboxylic acids. On basic hydrolysis, carboxylate ã Effect of electron withdrawing substituent ions are formed which can be further acidified on the acidity of carboxylic acids: Electron to form the corresponding carboxylic acids. withdrawing group increases the stability of Anhydrides can undergo hydrolysis reaction to carboxylate ion by delocalising the negative form the corresponding acid(s). charge and hence increases the acidic strength of carboxylic acids. H2O RCOOH + Cl– The effect of the following groups in the RCOCl – + increasing acidic strength of carboxylic acids O order is as follows: Ph < I < Br < Cl < F < CN OH /H2O RCOO– + Cl– H3O RCOOH < NO2 < CF3. Effect of number of electron withdrawing R —C H2O 2RCOOH O groups: As the number of electron withdrawing groups will increase, –I effect R—C thus also increases, increasing the acidic strength. O Effect of position of electron withdrawing • From esters: Acidic hydrolysis of esters directly group: As the distance between the electron give carboxylic acids while basic hydrolysis form withdrawing group and the carboxyl group carboxylates, which on further acidification gives of carboxylic acid group increases, the corresponding carboxylic acids. electron withdrawing influence decreases. + • Reactions involving cleavage of C–OH bond: Carboxylic acids on heating with mineral acids R—COO—R' H3O R—COOH + R′—OH such as H2SO4 or with P2O5 give the corresponding anhydrides as follows: R—COO—R' NaOH R—COO– Na+ + R′—OH ã Anhydride formation: + H3O RCOOH Physical Properties of Carboxylic Acids OO • Solubility: Carboxylic acids having upto 4 carbon H3C C+ C CH3 H+, D atom are soluble in water due to H-bonding OH HO or P2O5, D with water molecules. As the size of alkyl group increases the solubility of carboxylic acids in Ethanoic acid OO water or other polar solvents decreases because non-polar part i.e. the hydrocarbon chain length CH3 C C CH3 of the acid increases. O Ethanoic anhydride Aldehydes, Ketones And CArboxyliC ACids 283
ã Esterification: Carboxylic acids can be one carbon less than the parent acid. esterified with alcohols in the presence of a • Reactions involving substitution reactions mineral aacsidasucachtaalyssct.onTcheentrreaatcetdioHn2SocOc4uorsr of hydrocarbon part: HCl gas ã Hell-Volhard-Zelinsky reaction: Carboxylic acids having an a-hydrogen as follows: atom are halogenated at the a-position when treated with chlorine or bromine in the ã Carboxylic acids can react with PCl5, PCl3 presence of small amount of red phosphorus and SOCl2 to form acyl chlorides as follows: to give a-halocarboxylic acids. RCOOH + PCl5 → RCOCl + POCl3 + HCl 3RCOOH + PCl3 → 3RCOCl + H3PO3 RCOOH + SOCl3 → RCOCl + SO2 + HCl Reaction with awmitmh oanmiam(oNnHia3)t:oCaforrbmoxythliec ã acids can react corresponding ammonium salts which on further heating at high temperature give amides. ã Ring substitution in aromatic acids: CH3COOH + NH3 CH3COO– NH4+ D CH3CONH2 Aromatic carboxylic acids can undergo Ammonium acetate –H2O Acetamide Acetic acid electrophilic substitution reactions. Carboxyl COOH COO– NH4+ CONH2 group in benzoic acid is electron withdrawing + NH3 D group and it is meta directing in nature. –H2O COOH COOH Benzoic acid Ammonium benzoate Benzamide • Reactions involving COOH group: Conc. HNO3 ; Conc. H2SO4 ã Reduction: Carboxylic acids can be reduced NO2 to form alcohols in the presence of reducing COOH m-Nitrobenzoic acid agents like LiAlH4 or B2H6. COOH ã Decarboxylation: Sodium or potassium Br2/FeBr3 salts of carboxylic acids react with sodalime (NaOH + CaO in ratio of 3:1) which on Br heating gives hydrocarbons which contain m-Bromobenzoic acid ExErCIsE 8.2 Multiple Choice Questions (MCQs) (1 Mark) (i) Phenol and benzoic acid in the presence of 1. Which of the following substituent increases the NaOH acidic strength of carboxylic acid to the maximum extent? (ii) Phenol and benzoyl chloride in the presence of pyridine (i) Cl (ii) F (iii) Phenol and benzoyl chloride in the presence (iii) CN (iv) NO2 of ZnCl2 2. The correct order of increasing acidic strength is (iv) Phenol and benzaldehyde in the presence of .................... . palladium (i) Phenol < Ethanol < Chloroacetic acid < Acetic 4. Which is the most suitable reagent for the acid following conversion? O (ii) Ethanol < Phenol < Chloroacetic acid < Acetic acid CH3 CH CH CH2 C CH3 O (iii) Ethanol < Phenol < Acetic acid < Chloroacetic acid CH3 CH CH CH2 C OH (i) Tollens’ reagent (ii) Benzoyl peroxide (iv) Chloroacetic acid < Acetic acid < Phenol < (iii) I2 and NaOH solution Ethanol (iv) Sn and NaOH solution O 3. Compound Ph O C Ph can be prepared by the reaction of .................... . 284 Chemistry-12
Assertion-Reason Type Questions (1 Mark) 14. Give plausible explanation for the following: During the preparation of esters from a carboxylic Note: In the following questions, a statement of acid and an alcohol in the presence of an acid assertion followed by a statement of reason is given. catalyst, the water or the ester should be removed Choose the correct answer out of the following choices as soon as it is formed? [NCERT] on the basis of the above passage. Short Answer Type Questions-I (2 Marks) (i) Assertion and reason both are correct statements 15. Write IUPAC names of the following: and the reason is correct explanation of (i) CH3—CH—COOH assertion. (ii) Assertion and reason both are correct statements OH but reason is not correct explanation of assertion. (ii) CH3—CH2—CH—COOC2H5 (iii) Assertion is correct statement but reason is CH3 wrong statement. CH3 (iv) Assertion is wrong statement but reason is (iii) CH3—CH—CH—COOC2H5 correct statement. 5. Assertion: Compounds containing CHO group Br are easily oxidised to corresponding carboxylic acids. (iv) CH3—CH—CONH2 Reason: Carboxylic acids can be reduced to alcohols by treatment with LiAlH4. CH3 6. Assertion: The a-hydrogen atom in carbonyl 16. Complete the following reactions: compounds is less acidic. COOH Reason: The anion formed after the loss of (i) SOCl2 a-hydrogen atom is resonance stabilised. Heat COOH 7. Assertion: Methanal does not undergo Aldol (ii) C6H5—CH2—CH3 ? C6H5COOK Condensation. 17. Why is ester hydrolysis slow in the begining but Reason: Methanal has no alpha hydrogen. becomes faster after sometime? [DSB 2010] Very Short Answer Type Questions (1 Mark) 18. Give a chemical test to distinguish between the following compounds: 8. Write the IUPAC name of: [CBSE 2011] (i) Acetic acid and Formic acid. (i) (ii) Acetic acid and Benzoic acid 19. Although phenoxide ion has more number of resonating structures than carboxylate ion, yet carboxylic acid is a stronger acid than phenol. Why? [NCERT] (ii) 20. Write the IUPAC names of the following 9. Write the IUPAC name of: compounds: (i) PhCH2CH2COOH (ii) (CH3)2C CHCOOH CH3 NO2 COOH (i) [CBSE 2011C] (iii) COOH (iv) (ii) [CBSE 2014] O2N NO2 [NCERT] 10. Compare the strength of the following acids 21. Which acid among each pair of acids shown here would you expect to be stronger? (i) Formic acid (ii) Acetic acid (i) CH3CO2H or CH2FCO2H (iii) Benzoic acid (ii) CH2FCO2H or CH2ClCO2H (iii) CH2FCH2CH2CO2H or CH3CHFCH2COOH 11. Arrange the following in increasing order of acidic character: HCOOH, ClCH2COOH, CF3COOH, CCl3COOH (iv) F3C COOH 12. Write the structural formula of 2-phenylethanoic or acid. [CBSE 2013] H3C COOH 13. Write the structure of 2-hydroxybenzoic acid. [CBSE 2014] [NCERT] Aldehydes, Ketones And CArboxyliC ACids 285
Short Answer Type Questions-II (3 Marks) Tollens’ reagent and also undergoes Cannizzaro 22. Predict the products of the following reactions: reaction. On vigorous oxidation it forms benzene (i) 1, 2-dicarboxylic acid. Identify the compound. [NCERT] (ii) 32. An organic compound (A) (molecular formula C8H16O2) was hydrolysed using dilute H2SO4 to (iii) [CBSE 2022] form a carboxylic acid (B) and an alcohol (C). 23. Give chemical tests to distinguish between the Oxidation of (C) using chromic acid produces following pairs of compounds (B). (C) on dehydration can give but-l-ene. Write (i) Benzaldehyde and Benzoic acid (ii) Propanoyl chloride and Propanoic acid equations for the reactions involved. (iii) Ethanoic acid and Ethyl benzoate 24. How will you bring about following conversions 33. Arrange the following compounds in the increasing in not more than two steps: order to their property as indicated: (i) Propanoyl chloride to Dipropylamine (i) Acetaldehyde, Acetone, Di-tert.- butylketone, (ii) Propanoic acid to Propenoic acid Methyl tert.- butylketone (reactivity towards (iii) Benzoyl chloride to Benzonitrile HCN) 25. Why is carboxylic acid group in benzoic acid is m-directing? Support your answer with two (ii) CCHH23CCOHO2CHH,((BCrH)C3)O2COHHC, OCOHH3C,H(Br) examples. CH3CH2CH2COOH (acid strength) 26. Write balanced equations for the following (iii) B e n z o i c a c i d , 4 - N i t r o b e n z o i c a c i d , reactions? 3,4-Dinitrobenzoic acid, 4-Methoxybenzoic (i) Thionyl chloride reacts with benzoic acid acid (acid strength) [NCERT] (ii) Acetic acid is reacted with red phosphorus Long Answer Type Questions (5 Marks) and HI 34. Write the IUPAC name of the following compounds: (iii) Acetic acid is treated with Zinc metal 27. What happens when: (i) C6H5CH CHCOOH (ii) CH3CH CHCH CHCOOH (i) An aqueous solution of sodium acetate is (iii) CH3CH2CH— CH2COOH electrolysed CHO (ii) Calcium acetate is dry distilled (iv) CH3CH CHCOOH (iii) Sodium benzoate is heated with sodalime (v) (CH3)2—C—CH2—C—OH 28. Predict the products: OH O 35. Write balanced chemical reactions to bring about the following transformations: (i) K2Cr2O7 A SOCl2 B NH3 C NaOBr D (i) Butan-l-ol to butanoic acid H2SO4 CH3CH2OH (ii) Benzyl alcohol to phenylethanoic acid (ii) CH3CH2Cl KCN A OH – P2O5 C (iii) 3-Nitrobromobenzene to 3-nitrobenzoic acid B (iv) 4-Methylacetophenone to benzene-1, (iii) CH3COOH C2H5OH A (i) CH3MgBr B (i) CH3MgBr C 4-dicarboxylic acid Conc H2SO4 (ii) H2O/H+ (ii) H2O/H+ (v) Cyclohexene to hexane-1,6-dioic acid 29. Arrange the following compounds in the order of their increasing acidic strength: [NCERT] (i) Propanoic acid, chloroethanoic acid, 36. Show how each of the following compounds can 3-Bromopropanoic acid and Trichloroacetic be converted to benzoic acid: acid. (i) Ethyl benzene (ii) Acetophenone (ii) 2-Fluorobutanoic acid, 2-Iodobutanoic acid, (iii) Bromobenzene 2-Bromobutanoic acid and Butanoic acid. (iv) Phenylethene (styrene) (iii) Acetic acid, 2-Methylpropanoic acid, (v) Benzoic anhydride [NCERT] 2,2-Dimethylpropanoic acid. 37. How will you prepare the following compounds 30. How will you convert ethanal into the following from benzene? You may use any inorganic reagent compounds? and any organic reagent having not more than one (i) Butane-1,3-diol (ii) But-2-enal carbon atom. (iii) But-2-enoic acid [NCERT] (i) Methyl benzoate (ii) m-Nitrobenzoic acid 31. An organic compound with the molecular formula, (iii) p-Nitrobenzoic acid (iv) Phenyl acetic acid. C9H10O forms 2,4-DNP derivative, reduces (v) p-Nitrobenzaldehyde [NCERT] 286 Chemistry-12
Answers 8.2 1. (iv) 2. (iii) 3. (ii) due to the formation of ferric acetate. On the other hand, benzoic acid gives buff coloured 4. (iii) 5. (ii) 6. (iv) pofpfte. rwriitchbFeenCzol3astoel.ution, due to the formation 19. The resonating structures of phenoxide ion are: 7. (i) – ++ 8. (i) 3, 5-Dimethylphenyl ethanoate O OO (ii) Hex-2-en-4-ynoic acid – 9. (i) 3-Bromo-5-chlorobenzoic acid – (ii) 3-Hydroxybutanoic acid 10. Acetic acid < Benzoic acid < Formic acid 11. HCOOH < ClCH2COOH < CCl3COOH < CF3COOH 12. 13. –+ OO – 14. Formation of esters by the reaction of a carboxylic Now, the resonating structures of a carboxylate acid with an alcohol, in the presence of an acid ion are: catalyst is a reversible reaction: Therefore, to shift the equilibrium in the forward Among them carboxylate ion is more stabilised direction, the water or ester should be removed because the negative charge is delocalised as soon as it is formed. on the more electronegative oxygen atom, whereas in phenoxide ion, it is delocalised on the 15. (i) 2-Hydroxypropanoic acid less electronegative carbon atom. This makes (ii) Ethyl 2-methylbutanoate carboxylic acid a stronger acid than phenol. (iii) Ethyl 3-bromo-2-methylbutanoate 20. (i) 3-Phenylpropanoic acid. (ii) 3-Methylbut-2-en-oic acid. (iv) 2-Methylpropanamide (iii) 2-Methylcyclopentanecarboxylic acid 16. (i) COOH + 2SOCl2 Heat (iv) 2,4,6-Trinitrobenzoic acid COOH 21. (i) FCH2COOH (due to –I effect of F) (ii) FCH2COOH (due to stronger –I effect of F) Phthalic acid COCl (iii) CH3CHFCH2COOH (Q inductive effect decreases with distance) + 2SO2 + 2HCl COCl (iv) F3C COOH (due to stronger –I effect of F) Phthaloyl Chloride (ii) C6H5–CH2–CH3 KMnO4 / KOH C6H5COOK Heat 17. An ester on hydrolysis forms an alcohol and an 22. (i) CH3—C O (i) NH2—NH2 acid. (ii) KOH, glycol, ∆ CH3 CH3—CH2—CH3 A small amount of dil.H2SO4 is added in the (ii) C6H5COCH3 NaOH + I2 beginning in order to start the reaction. As the reaction proceeds, a carboxylic acid (R—COOH) CHI3 + C6H5COONa is produced which acts as auto-catalyst. As the amount of carboxylic acid produced increases, the (iii) CH3COONa NaOH + CaO rate of ester hydrolysis also increases. ∆ 18. (i) Formic acid reduces Fehling’s solution and CH4 + Na2CO3 Tollens’ reagent, while acetic acid does not give these tests. 23. (i) On adding NaHCO3 benzoic acid will give brisk effervescence due to the formation (ii) fOonrmtrsebaltomodenrtedwoitrhwFineCe lr3esdocluoltoiounre, adcseotliuctaiocnid, of CO2. Benzaldehyde will not react with NaHCO3. (ii) ObrnicakddefifnegrvNeasHceCnOce3,dPureoptaontohiec acid will give formation of wCOith2 while propanoyl chloride will not react NaHCO3. Aldehydes, Ketones And CArboxyliC ACids 287
(iii) On adding NaHCO3, Ethanoic acid will give 27. (i) 2CH3COONa(aq) 2CH3COO–+ 2Na+ brisk effervescence due to the formation of At anode: 2CH3COO– – 2e– æÆ CO2 whereas ethyl benzoate will not react CH3 + 2CO2 with NaHCO3. CH3 O At cathode: 2H+ + 2e– æÆ H2(g) 24. (i) CH3CH2—C—Cl + CH3CH2CH2NH2 O O CH3—CH2—C—NHCH2CH2CH3 Na/C2H5OH (ii) (CH3COO)2Ca Dry CH3—C—CH3 + CaCO3 4 (H) distillation CH3CH2CH2NHCH2CH2CH3 COONa (ii) CH3CH2COOH P4/Cl2 Cl (iii) + NaOH + CaO ∆ + Na2CO3 CH3—CH—COOH KOH (alc.) 28. (i) CH3CH2OH K2Cr2O7 CH3COOH SOCl2 CH2 CH—COOH H2SO4 ‘A’ (iii) C6H5COCl NH3 C6H5CONH2 P2O5 C6H5C CH3COCl NH3 CH3CONH2 ∆ N 25. It is because there is +ve charge on three out ‘B’ ‘C’ of five resonating structures of benzoic acid at (ii) CH3CH2Cl KCN CH3CH2CN OH – o- and p-position and electron density is more ‘A’ at m-position hence electrophilic substitution O reaction will take place at meta position, e.g. CH3CH2—C—NH2 P2O5 CH3CH2C º N COOH COOH O (iii) CH3COOH C2H5OH CH3—C—OC2H5 (i) CH3MgBr Conc H2SO4 (ii) H2O/H+ ; ‘A’ + Br2 FeBr3 COOH Br O OH COOH CH3—C—CH3 (i) CH3MgBr CH3—C—CH3 (ii) H2O/H+ CH3 ‘B’ ‘C’ + conc. HNO3 conc H2SO4 NO2 29. (i) C H 3C H 2C O O H < B r C H 2C H 2C O O H < ClCH2COOH < Cl3CCOOH 26. (i) (ii) (ii) CH3CH2CH2COOH < CH3CH2CHICOOH < (ii) CH3CH2CHBrCOOH < CH3CH2CHFCOOH (iii) (CH3)3CCOOH < (CH3)2CHCOOH < CH3COOH 30. (i) CH3CHO AldoldCilo.NndaeOnHsation→ CH3 CH CH2CHO RNedauBcHtio4 n→ CH3 CH CH2 C| H2 | | Ethanal OH OH OH Butane-1,3-diol (ii) CH3CHO AldoldCilo.NndaeOnHsation→ CH3 CH CH2CHO H−3HO2+O,∆→ CH3CH=CHCHO | Ethanal OH But-2-enal (iii) CH3CHO AldoldCilo.NndaeOnHsation→ CH3 CH CH2CHO H−3HO2+O,∆→ CH3CH=CHCHO | Ethanal OH But-2-enal Ag(oNxHid3a)t2io+nOH− → CH3CH=CHCOOH But-2-enoic acid 288 Chemistry-12
[O] COOH (1,2-Benzene dicarboxylic acid) (K2Cr2O7/H2SO4 COOH conc.) COO– CHO +– CH2CH3 (2-Ethylbenzoate) NO2 31. CH2CH3 [Ag(NH3)2] OH (Tollens' reagent) CH NHN NO2 2-Ethylbenzaldehyde 2,4-DNP CH2CH3 (2,4-DNP derivative) CH2OH COONa CH2CH3 CH2CH3 conc. NaOH + Cannizzaro Reaction O + HOH/H 32. CH3CH2CH2 C OCH2CH2CH2CH3 (hydrolysis) CH3CH2CH2COOH + CH3CH2CH2CH2OH (A) Butyl butanoate (B) Butanoic acid (C) Butan-1-ol CH3CH2CH2CH2OH CrO3/H2SO4 CH3CH2CH2COOH CH3CH2CH CH2 (Oxidation) But-1-ene (C) Butan-1-ol (B) Butanoic acid Heat above 443 K conc. H2SO4 33. (i) Di-tert-butylketone < Methyl tert-butylketone 35. (i) CH3CH2CH2CH2OH JCornOe3s−rHea2gSeOn4t → < Acetone < Acetaldehyde Bu tan −1 − ol CH3CH2CH2COOH (The reactivity towards addition reaction with HCN will increases as the +I effect of Butanoic acid the alkyl group will decrease.) CH2OH CH2Br (ii) (CH3)2CHCOOH < CH3CH2CH2COOH < (ii) HBr KCN CH3CH—CH2COOH < CH3CH2CHCOOH or PBr3 Br Br Benzyl Benzyl CH2COOH alcohol bromide (The +I effect will decrease while –I effect will increase the acidic strength of Br CH2CN —COOH group. Further –I effect decreases with distance). + (iii) 4-Methoxybenzoic acid < Benzoic acid < H2O, H 4-Nitrobenzoic acid < 3, 4-Dinitrobenzoic acid D Benzyl cyanide Phenyl ethanoic acid MgBr (Electron donating group decreases the acidic (iii) Mg CO2 strength while electron withdrawing group Dry ether (dry ice) increases the acidic strength). NO2 AdditionNO2 34. (i) 3-Phenylprop-2-en-1-oic acid (ii) Hex-2,4-dien-1-oic acid 3-Nitrobromo- product benzene COOMgBr COOH (iii) 3-Formylpentan-1-oic acid + (iv) But-2-en-1- oic acid (v) 3-Hydroxy-3-methyl butanoic acid H2O, H (Hydrolysis) NO2 3-NitrobenzNoicO2 acid Aldehydes, Ketones And CArboxyliC ACids 289
COCH3 COOK COOH ( )(v) H2O→ 2C6H5COOH C6H5CO 2O (iv) KMnO4/KOH Dil. H2SO4 Benzoic acid Benzoic anhydride Br MgBr CH3 COOK COOH 37. (i) Br2 Mg (i) CO2 FeBr3 Dry ether (ii) H3O+ 4-Methyl Dipotassium Benzene-1,4- acetophenone benzene-1,4- dicarboxylic acid COOCH3 dicarboxylate (Terephthalic acid) Benzene Bromobenzene COOH (v) CH3OH (excess) conc. H2SO4. heat Benzoic acid Methylbenzoate CH2CH3 –+ COOH Br MgBr COOK 36. (i) KMnO4-KOH + (ii) Br2 Mg (i) CO2 D (ii) H3O+ H3O FeBr3 (Dry ether) (hydrolysis) COOH Ethyl Benzene COOH benzene Benzoic acid COCH3 –+ COOH conc. HNO3 conc. H2SO4. heat COOK m-Nitrobenzoic acNidO2 (ii) KMnO4-KOH + CH3 D Acetophenone H3O COCH3 (hydrolysis) or – + Benzoic acid (iii) CH3Cl conc. HNO3 COOH Anhyd. AlCl3 conc. H2SO4, D COONa I2/NaOH + Benzene Toluene Iodoform reaction H3O CH3 CH3 (hydrolysis) NO2 Br MgBr + Separated by filtration (-o-nitrotoluene) Mg CO2 o-nitrotoluene Dry ether (Dry ice) (iii) NO2 (Minor product) (Liquid) p-nitrotoluene (Major product) Bromobenzene Phenyl magnesium (Solid) bromide CH3 COOH COOMgBr COOH + (i) KMnO4/KOH, heat (ii) dil. H2SO4 H3O –Mg (OH)Br NO2 NO2 (Hydrolysis) p-Nitrobenzoic acid p-nitrotoluene Benzoic acid CH CH2 COOK (iv) KMnO4-KOH CH3 D + HCOOK CH3Cl/AlCl3 Br2, Heat, hn Phenyl ethene COOH (iv) or NBS, hn (Styrene) Friedel-Crafts Alkylation Toluene Benzene + CH2Br CH2CN CH2COOH H3O + HCOOH KCN (alc.) H+, H2O (Hydrolysis) Heat Methanoic Benzoic acid acid Benzylbromide Benzylcyanide Phenylacetic acid 290 Chemistry-12
CH3 CH3 CH3 CH3 (v) CH3Cl conc. H2SO4 + NO2 AlCl3 conc. HNO3, ∆ Benzene Separated by filtration Toluene (-o-nitrotoluene) NO2 NO2 CHO (i) CrO2Cl2/CS2 or CrO3/(CH3CO)2O (ii) H3O+ (Etard reaction) NO2 p-Nitrobenzaldehyde Case based questions 1. Case Study Give product of the following reaction: O O CHO + R1 CH2R2 + Ar—CHO Na2CO3 (cat) Na2CO3 (cat) ? H2O, CH3 CH2CH3 H O, rt 2 rt (Room temperature) O OH O CH O OH (a) CH3 CH 3 R1 Ar R2 3 (b) CH3 O O An environmentally benign and efficient process for the preparation of b-hydroxyl ketones (c) CH3 (d) OH was developed by the practical cross-aldol CH3 reactions of 2-acetylpyridine, acetophenone, (iii) Which of the following is the product of the given and cyclohexanone with 4-nitro-, 3-nitro-, and reaction: 2-nitrobenzaldehydes in water catalyzed by Na2CO3 in very high yields. (Reference: Guan-Wu Wang, Ze Zhang, and Ya-Wei Dong, (2004). Environmentally Friendly and Efficient Process for the Preparation of b-Hydroxyl Ketones, Org. Proc. Res. Dev. 8, 1, 18–21) The following questions are multiple choice (a) (b) questions. Choose the most appropriate answer: (c) (d) (i) Which of the following is a b-hydroxyl ketone? (iv) The reagent which does not react with both, acetone and benzaldehyde. O OH OH (a) Sodium hydrogensulphite (b) Phenyl hydrazine (a) (b) (c) Fehling’s solution (d) Grignard reagent O 2. Case Study OO An efficient and more environmentally benign method has been developed to reduce aldehydes (c) (d) and ketones to alcohols, using zinc and diammonium hydrogen phosphite, as a reducing O O OH Aldehydes, Ketones And CArboxyliC ACids 291 (ii) What is the IUPAC name of ? (a) 4-hydroxy-2-butanone (b) 4-hydroxy-2-pentanone (c) 1-hydroxy-2-pentanone (d) 3-pentanone-1-hydroxy OR
agent in a toluene/water media at reflux condition. Give product of the reaction: The system is highly efficient in reducing both O nitro and carbonyl groups whereas most of the existing methods cannot reduce both of them CH (NH4)2HPO3 / H2O, Zn simultaneously. Other functional groups viz., –Cl, 3 –Br, –CH3, –OCH3, and –OH are tolerated. rt / Reflux, Toluene O (a) CH3 (b) R (NH4)2HPO3 / H2O, Zn OH rt (Room temperature) / Reflux, Toluene (c) CH3 (d) X OH R X where, R = –H, –CH3 (iv) , X = –Cl, –Br, –OH, –CH3, –NO2, –OCH3 A will be (Source: K. Anil Kumar and D. Channe Gowda, OH Reduction of aldehyde and ketones to corresponding (a) H OH alcohols using diammonium hydrogen phosphite and (b) commercial zinc dust, E-Journal of chemistry 2011, 8(1), 49–52) The following questions are multiple choice (c) (d) questions. Choose the most appropriate answer: 3. Case Study Facile and selective reduction of aromatic (i) What will be the product when benzaldehyde is aldehydes as well as aliphatic aldehydes to alcohols was achieved using formic acid as the subjected to above reaction conditions? hydrogen donor in the presence of a catalytic abmotohuhnytdorfoPgedn(OaAtocm)2sainndtChey3fPo.rmItiwc aacsidfomunodletchualet (a) Benzyl alcohol (b) Phenol can serve as the hydride source. (c) Benzoic acid (d) Toluene (ii) Give product of the reaction: CHO (NH4)2HPO3 / H2O, Zn OH rt / Reflux, Toluene OH CH2OH CHO (a) (b) (Source: Zhiyong Yang, Jidan Liu, Qingwen Gui, Xiang Chen, ZeTan and Ji-cheng Shi, (2014), Pd-Catalyzed OH Reduction of Aldehydes to Alcohols using formic acid as the Hydrogen Donor. Synthetic communications 44(2).) OH CHO CH3 (c) (d) The following questions are multiple choice questions. Choose the most appropriate (iii) Give product of the reaction: answer: CHO (i) The Pd based catalyst mention in the study can be used to convert: (NH4)2HPO3 / H2O, Zn NO2 rt / Reflux, Toluene CH2OH CH2OH (a) Propanol to Propanal (a) (b) (b) Propanal to Propanol NO NH (c) Propanoic acid to Propane 2 2 (d) Propanal to Propene NH (ii) When benzaldehyde is subjected to the conditions 2 given above, the product formed will be CH CHO 3 (c) (d) (a) Benzyl alcohol (b) Phenol NH (c) Benzoic acid (d) Benzene 2 OR OR 292 Chemistry-12
Predict the product of reaction: (i) Which of the following is an a, b-unsaturated (a) R—CH2—COOH (b) ketone? (c) R—CH = CH2—OH (d) (a) O O (b) O (c) (d) (ii) Give the product formed in the following reaction: (iii) Acetaldehyde on treatment with Pd-based catalyst gives a compound ‘A’ which on reaction with chromic acid (H2CrO4) gives compound ‘B’. O O Compound B is (a) (a) a carboxylic acid (b) a ketone (b) (c) an alcohol (d) an alkane (iv) An organic compound ‘X’ with molecular formula C4H8O on reaction with Pd-based catalyst gives compound ‘Y’, which undergoes dehydration on (c) (d) reaction with H2SO4 and gives compound Z. The (iii) Give the product formed in the following reaction: compound Z is O CH2—OH (a) cis-2-butene (b) trans-2-butene (c) Butane (d) Butanol 4. Case Study ()n + Fe / Phen (5/6 mol%) a, b-unsaturated ketones are widely present in OMe various pharmaceutically important plants, and O are extensively used as life-saving drugs. Below are the schemes established for synthesis of a, b-unsaturated ketones which are highly (a) ( )n selective, cost-efficient and simple as compared OMe to the conventional methods. O OMe O M (b) ( )n O 1. + R OH O (c) ( )n O R OMe (M = Ru, Pd, Pt) O 2. ()n + R OH Fe / Phen (d) ( )n OMe (5/6 mol%) OR O Give the product formed in the following reaction: ()n R O (Reference: Motahar SK, Ashish Kumar, Jagadish Fe / Phen (5/6 mol%) Das, Debasis Banerjee, (2020). A simple iron-catalyst for alkenylation of ketones using primary alcohols, + CH3CH2OH Molecules 2020, 25(7), 1590) O The following questions are multiple choice O CH2CH3 questions. Choose the most appropriate (a) (b) answer: Aldehydes, Ketones And CArboxyliC ACids 293
O O CH—CH (a) 3 O (c) O (d) (b) O OH CHCH O (d) 3 (c) (iv) Give the product formed in the following reaction: O OH Ru + Answers 1. (i) (a) (ii) (b) or (a) (iii) (a) (iv) (c) 3. (i) (b) (ii) (a) or (b) (iii) (a) (iv) (b) 2. (i) (a) (ii) (a) (iii) (b) or (c) (iv) (a) 4. (i) (a) (ii) (d) (iii) (a) or (c) (iv) (a) Analogy based questions (i) A : Reacts with monohydric alcohols 1. Which of the following analogies is correct? B : Do not react with monohydric alcohols (i) Electron withdrawing group : – I :: Electron donating group : – NO2 (ii) A : Can be reduced to alcohol (ii) Aldehydes with a-H atom : Gives Aldol B : Cannot be reduced to alcohol Condensation :: Aldehydes without a-H atom : Gives Cannizarro reaction (iii) A : Do not give Tollens’ test B : Give Tollens’ test (iii) Mild oxidising agent : PCC :: Strong oxidising agent : Cu/573 K (iv) A : Can be oxidised with KMnO4 B : Cannot be oxidised with KMnO4 (iv) Formic acid : Does not give Tollens’ test :: Formaldehyde : Gives Tollens’ test 1. (ii) Answers 2. Complete the following analogy 2. (i) Aldehydes : A :: Ketones : B Matching type question 1. Match the common names given in Column I with the IUPAC names given in Column II. Column I (Common names) Column II (IUPAC names) A. Cinnamaldehyde (1) Pentanal B. Acetophenone (2) Prop-2-enal C. Valeraldehyde (3) 4-Methylpent-3-en-2-one D. Acrolein (4) 3-Phenylprop-2-enal E. Mesityl oxide (5) 1-Phenylethanone Code: (i) A (4) B (5) C (1) D (3) E (2) (ii) A (4) B (5) C (1) D (2) E (3) (iii) A (5) B (4) C (2) D (1) E (3) (iv) A (5) B (4) C (1) D (3) E (2) Answers 1. (ii) Chemistry-12 294
Quick revision notes using acyl halides in the presence of AlCl3 • Inaldehydes,thecarbonylgroup( C=O)isattached (anhydrous). with one hydrogen and one alkyl/aryl group. e.g. • Both aldehydes and ketones can undergo O nucleophilic addition reaction on the carbonyl C-atom with a number of nucleophiles such as CH3—C—H (ethanal) , HCN, NaHSO3, CH3OH, CH3MgBr, etc. • In ketones, the carbonyl group ( C = O) is attached • Aldehydes and ketones having a-hydrogen with two alkyl/ar yl groups, e.g. CH3 C==O atoms are acidic in nature and undergoes aldol CH3 condensation reaction in the presence of a base to (Acetone) and C6H5 give a-hydroxyaldehydes and a-hydroxyketones C6H5 C==O (Benzophenone) (Ketol), respectively which on dehydration gives a, b-unsaturated aldehydes and ketones. • As ‘O’-atom is more electronegative than ‘C’-atom, therefore C = O bond is polar in nature. • Aldehydes and ketones without a-H-atom can undergo Cannizarro reaction in the presence • The polar nature of C = O bond is responsible for of conc. alkali to form alcohols and sodium or the higher boiling point of aldehydes and ketones potassium salt of acids. than the corresponding hydrocarbons. • C = O group in aldehydes and ketones can be • Lower members of aldehydes and ketones can reduced into methylene group by Clemmensen form H-bond with water molecules and are reduction using Zn (Hg) or Wolff Kishner thus water soluble, e.g. 40% aqueous solution of reduction using NH2–NH2, KOH and glycol. formaldehyde is called formaline. • C = O group of aldehydes can also be oxidised • However with increase in the hydrocarbon chain to form carboxylic acids by mild oxidising agents length steric factor comes into play, which makes like Tollens’ reagent and Fehling’s solution. them more soluble in organic solvents and not Ketones do not react because they itself act as in water. This is due to increase in hydrocarbon mild reducing agents. part, which is hydrophobic. • Tollens’ reagent and Fehling’s solution are used • Aldehydes and ketones are named according to distinguish between aldehydes and ketones. to the IUPAC system by replacing the ‘e’ of the corresponding hydrocarbon with ‘al’ and • Formaldehyde has high industrial importance as it is used to prepare bakelite, to preserve ‘one’, respectively e.g., is methanal, biological specimens. is propanone. • Ketones too are used as important industrial solvents and as catalysts to carry out various • Aldehydes and ketones can be prepared by chemical reaction in organic chemistry. Acetone oxidation of primary and secondary alcohols, is used as a solvent in many industries. respectively using mild oxidising agents like PCC, CrO3, or Cu /573 K. • Carboxylic acids are the compounds having • Aldehydes and ketones can also be prepared ‘—COOH’ functional group, e.g. CH3COOH by the reduction of acyl halides selectively and (ethanoic acid). by using dialkylcadmium as another reagent respectively, aldehydes are selectively prepared • They are named by replacing ‘e’ of the by Rosenmund reduction. corresponding hydrocarbon with ‘oic acid’, e.g. HCOOH is methanoic acid. • Aromatic aldehydes may also be prepared by oxidation of (i) methylbenzene using chromyl • The carbonyl group in carboxylic acids has C- and cphrelosreindcee(oEftaarcdetirceaacnthioynd)riodreC, (riOi)3biyn HCl, in the O-atoms in one plane (sp2 hybridised carbon) and formylation carbon is less electrophilic than the carbonyl of arenes with CO and HCl in the presence of C-atom of aldehydes and ketones because it is anhyd. hAyldCrlo3ly(sGisatotfebrmenaznanl Koch reaction) and attached to –OH group. (iii) by chloride. • Acids are generally prepared by strong oxidation • Aldehydes and ketones can also be prepared by of primary alcohols or by oxidation of aldehydes ozonolysis of alkenes followed by reduction with and ketones, and by the acidic hydrolysis of Zn and H2O. nitriles (cyanides). • Aromatic ketones can be prepared in an efficient • They are also prepared by treatment of CO2 gas way by using Friedal-Crafts acylation reaction (dry ice) with Grignard reagents and by hydrolysis of amides, acyl chlorides, anhydrides and esters. Aldehydes, Ketones And CArboxyliC ACids 295
• Aromatic carboxylic acids are prepared by side effectively as compared to less electronegative chain oxidation of Benzyl alcohol, its derivatives and from alkyl benzenes, e.g. Toluene, ethyl carbon atom in case of phenols and alcohols. benzene, n-propyl benzene, etc. • Electron withdrawing group like –Cl, –Br, –F, • In Hell-Volhard-Zelinsky reaction (HVZ), carboxylic acids undergoes a-halogenation a–cIi,d–s,NwOh2ileenehleacntcroens the acidity of carboxylic with Cl2, Br2 in the presence of red phosphorus. c–aCr2bHo5x,y–lOicHa,ci–dOs.CH3, er.egl.edaescinregagsreosutpheliakceid–iCtyHo3f, Carboxylic acids are reduced to primary alcohols using LiAlH4 or B2H6 in ether solution. • Besides, aromatic carboxylic acids can also • Lower members containing —’COOH’ group are undergo ring substitution reactions generally at water soluble due to H-bonding and they ionise in aqueous solution however with increase in m-position with respect to the COOH group, as length of the hydrocarbon chain, the acids become –COOH group is meta-directing in nature because insoluble due to hydrophobic interactions of alkyl/ aryl group of carboxylic acids. it is electron withdrawing. • Carboxylic acids have higher boiling point than • Formic acid (or Methanoic acid, HCOOH) is the corresponding aldehydes, ketones, alcohols and simple hydrocarbons, due to extensive highly useful in rubber, textile, dyeing and intermolecular H-bonding, which also results in dimerisation of carboxylic acids in many cases. electroplating industry. It is a strong reducing • They are less soluble in non-polar organic solvents asiglveenrt.mIitrrdoerctoelsotuwriistehsTaoclilednifsi’erdeaKgMenntO. 4, gives like benzene, ether, etc. due to polarity in lower carboxylic acids. • Acetic acid is also used as an industrial solvent • Carboxylate ion is stabilised by resonance. and in the production of vinegar. Therefore, carboxylic acids are more acidic than phenol and alcohols because negative charge • Adipic acid (used in manufacture of Nylon-6, 6) is delocalised over two oxygen atoms more is of great importance in the polymer industry. • Higher members (called fatty acids) are used in the preparation of soap and detergents. • Carboxylic acids can react with alcohols to form esters, which are highly useful in the perfume industry, ice-cream, cold drinks and as artificial flavours. Important reactIons 1. CH3CH2OH Cu/573K O 6. + O3 CH3—C—H O Zn/H2O O + H2O2 OO 2. 3. Rosenmund Reduction: 7. HC CH + H2O H2SO4 HgSO4 O CH2 CHOH CH3—C—H 8. CH3—C CH + H2O H2SO4 HgSO4 O OH 4. CH3—C—CH2 CH3—C—CH3 CHCl2 OH CHO CH 5. Ozonolysis: 9. + 2KOH(aq) OH CH3—CH CH2 + O3 –H2O O Zn/H2O CH3— CH CH2 OO 10. CH3COO Ca Dry O CH3—C—H + H—C—H + H2O2 distillation CH3—C—CH3 + CaCO3 CH3COO OO 296 Chemistry-12
O O O OH H2O/H+ CH3—C—CN 11. CH3—C—O O—C—H Heat 20. CH3—C—H + HCN CH3—C—O Ca + Ca O—C—H H O O O (2-Hydroxypropanenitrile) (Optically active) OH O 12. Stephen reaction: 2CH3—C—CH3 + 2CaCO3 CH3—C—C—OH CH3C N SnCl2 + HCl CH3—CH NH H2O/HCl H O 2 [H] Lactic acid (2-Hydroxypropanoic acid) CH3—C—H + NH4Cl O (Optically active) 13. CH3—CH CH—CH—CH2—C N (i) DIBAL-H 21. CH3—C—CH3 + HCN (ii) H2O OH Hex-4-en-1-nitrile O CH3—C—CH3 H2O/H+ CH3—CH CH—CH2—CH2—C—H CN OH Hex-4-en-1-al O CH3—C—CH3 14. CH3—CH2—CH2—CH2—C—OC2H5 (i) DIBAL-H COOH (ii) H2O Ethyl pentanoate O O 22. H—C—H + CH3OH HCl(g) CH3—CH2—CH2—CH2—C—H + C2H5OH OH OCH3 Pentanal Ethanol H—C—H + CH3OH H—C—H OCH3 15. CH3—C N + CH3MgBr HCl(g) OCH3 (Hemiacetal) CH3 CH3 1-Methoxy methanol (Acetal) CH3—C NMgBr H2O/H+ CH3—C Br CH3 O + Mg NH2 O CHO 23. CH3—C—H + CH3OH HCl(g) 16. Etard Reaction: (i) CrO2Cl2/CS2 OH OCH3 (ii) H2O/H+ CH3—C—H CH3—C—H + CH3OH HCl(g) OCOCH3 CH3 CH OCH3 OCH3 OCOCH3 (1-Methoxy ethanol) (1, 1-Dimethoxy ethanol) 17. CrO3/(CH3CO)2O H2O/H+ O OMgBr 273-278K CH3—C—H H2O/H+ ∆ 24. CH3—C—H + CH3MgBr CHO CH3 OH 18. Friedel-Crafts Acylation: + 2CH3COOH CH3—CH—CH3 O O C CH3 25. CH3—C—CH3 + NaHSO3 + HCl ONa OH CH3—C—CH3 O Proton transfer + CH3—C—Cl AlCl3 CH3—C—CH3 OSO2Na OSO2Na Acetophenone H O + H2NH CH3—CH NH H2/Ni 19. Gatterman-Koch Reaction: 26. CH3—C Ammonia Acetaldimine CH3CH2NH2 CH3 CH3 CH3—C NOH 27. CH3—C O + H2NOH hydroxylamine Aldehydes, Ketones And CArboxyliC ACids 297
35. Cross-Aldol Condensation (Two different aldehydes with a-hydrogen): OH– CH3CHO + CH3CH2CHO 28. OH O OH O CH3—CH—CH2—C—H + CH3—CH2—CH—CH—C—H H O + H2N—NH2 CH3—CH N—NH2 OH O CH3 OH O 29. CH3—C Hydrazine Acetaldehyde hydrazone + CH3—CH—CH—C—H + CH3—CH2—CH—CH2—C—H H CH3 30. C6H5—C O + H2 N—NH—C6H5 36. Claisen Condensation (Similar to Aldol Condensation with one aliphatic and other Phenyl hydrazine aromatic aldehyde): C6H5CH N—NHC6H5 O Benzaldehyde phenylhydrazone CH3 C6H5—C—H + CH3CHO OH– 31. CH3—C O + H2 N—NH Benzaldehyde Acetaldehyde NO2 OH O NO2 C6H5—CH—CH2—C—H OH– 2, 4-DNP 3-hydroxy-3-phenylpropanal O CH3 C6H5—CH CH—C—H H2 / Ni CH3—C N—NH NO2 3-Phenylprop-2-en-1-al C6H5CH2CH2CH2OH 3-Phenylpropanol NO2 CHO CHO (Orange ppt) Acetone 2, 4-Dinitrophenylhydrazone HO 37. Br2 Br 32. CH3—C O + H2 N—NH—C—NH2 FeBr3 Semicarbazide O CH3—CH N—NH—C—NH2 38. Acetaldehyde semicarbazone 39. Clemmensen Reduction: 33. Cannizzaro’s reaction (Aldehydes with no O a-hydrogen): Zn(Hg) H 2H—C ==O conc. NaOH CH3OH + HCOONa CH3—C—H conc. HCl CH3—CH3 + H2O O 40. Wolff-Kishner Reduction: conc. NaOH O 2C6H5—C—H CH3—C—CH3 NH2–NH2, KOH CH3—CH2—CH3 + H2O ethylene glycol, ∆ O 41. Tollens’ test: C6H5CH2OH + C6H5—C—ONa CH3CHO + 2 Ag (NH3 )2 + + 3OH− → 34. Aldol Condensation (Aldehydes with atleast CH3COO− + 2Ag + 2H2O + 4NH3 one a-hydrogen): 42. Fehling’s test: O OH– OH O OH– CH3CHO + 2Cu2+ + 5OH− → 2CH3—C—H ∆ CH3COO− + Cu2O + 3H2O CH3—CH—CH2—C—H O ( )Red-brown 3-Hydroxy butanal ppt CH3—CH CH—C—H 43. CH3CH2OH (i) alkaline KMnO4 O (ii) H2SO4 CH3—C—OH + H2O But-2-en-1-al 298 Chemistry-12
CH2OH COOH CH2CH3 COOH 44. (i) alkaline KMnO4 + H2O 53. + 6[O] KMnO4, KOH + CO2 + H2O (ii) H2SO4 heat O 54. CH3COOH + PCl5 CH3COCl + POCl3 + HCl 55. C6H5COOH + SOCl2 45. CH3—C—CH2—CH2—CH3 K2Cr2O7 56. CH3COOH + NH3 C6H5COCl + SO2 + HCl conc. H2SO4 CH3COONH4 heat CH3COOH + CH3CH2COOH O O C CH3 COOH CH3—C—NH2 + H2O 46. K2Cr2O7 + CO2 + H2O 57. CH3COOH + C2H5OH conc. H2SO4 conc. H2SO4 CH3COOC2H5 + H2O O 58. Hell-Volhard-Zelinsky reaction: 47. CH3—C—OH LiAlH4 CH3CH2OH O Cl O O O CH3—C—OH Cl2 CH2—C—OH CH3—C—OMgBr redP4 48. CH3MgBr + C O H2O/H+ Ethanoic acid 2-Chloroethanoic acid O CH3—C—OH 59. O O 60. Decarboxylation: H+ 61. Kolbe Electrolysis: 49. CH3—C—OC2H5 + H2O CH3—C—OH + C2H5OH COOH COOH 50. + Br2 FeBr3 Br COOH COOH 51. conc. H2SO4 conc.HNO3 NO2 CH3 COOH 52. + 3[O] KMnO4, KOH COOH COOH heat 62. + conc.H2SO4 heat + H2O 63. CH3COOH + 6HI red P4 SO3H CH3—CH3 + 3I2 + 3H2O common errors errors correctIons (i) Students generally commit mistakes in (i) Schiff’s reagent, Fehling’s test, Tollens’ test are understanding about the distinction test of some tests which are generally show positive aldehydes and ketones results with aldehydes and not with ketones. (ii) Students generally write wrong distinctive test (ii) Formic acid can reduce Tollens’s reagent but for formic acid and acetic acid. acetic acid cannot. (iii) Students are unable to understand about the (iii) Though both are resonance stabilised but in acidic strength of carboxylic acid and phenol. carboxylic acids the resonance structures are more stable due to negative charge reside on more electronegative oxygen atom unlike electropositive carbon atom in phenols. Aldehydes, Ketones And CArboxyliC ACids 299
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